Is it still possible to optimize construction financing?

Hello everyone,
I am completely new here and, together with my girlfriend, share the dream of having our own four walls like many others here. Since we are still at the very beginning of our considerations, please forgive me if I forget something.
Because neither of us is a high earner and we want to stay realistic, we have already excluded a new build and want to buy an existing property. Specifically, it should be a terraced house or a semi-detached house.
We live in Magdeburg and the house should also be located in the vicinity of Magdeburg. The prices here are still quite reasonable, so you can get a house with a little land from the late '90s/around 2000 for about €120,000 – 150,000.
But first, a brief overview of our rough key data:
Income:

[*]My income: approx. €1800 (x13)
[*]Girlfriend’s income: approx. €1600 (x13 – 30h position), prospectively full-time position about €2000

Expenses: (only mine – why listed below)

[*]Warm rent including all insurances: just under €400 (we share almost €800 in total. Breakdown as follows: €426 cold rent, €192 additional costs, the rest for insurances, GEZ, internet & co.)
[*]Insurance and tax for car and motorcycle: €110
[*]Fuel costs: €80
[*]Mobile phone costs: €20
[*]Household account for groceries & co.: €150
[*]Expenses for leisure activities: €140
[*]Private pension: €110
[*]Securities savings plan: €100

[*]Total monthly expenses a little over €1100/month

Why have I only listed my expenses? My girlfriend has finished her studies and will start additional training in October, which is why she will have to reduce to 20 hours temporarily. Ergo, I am structuring a possible financing so that it is initially borne by me alone. This is also better if one earners is unavailable for whatever reason.

Schedule & capital:
I plan to buy the house within the next 2 – 5 years. But actually, I don’t want to push the 5 years. I am rather aiming for about 3 years. Currently, I can provide about €15,000 in equity. Then there are no reserves left. As an "investment" I still have my motorcycle. A realistic selling price is currently about €3000.

Planned loan:
The amount of my loan should under no circumstances be higher than €150,000. With the necessary 20% equity, €15,000 are still missing. Since current expenses still leave enough room to build reserves, I imagine a feasible loan rate of no more than €600. Since I am already 31 years old, I definitely want to avoid paying off for 30 years. Ideally, it would be 20 years, but a maximum of 25 years.

What do you think of the plan? Especially regarding saving the €15,000 in such a short time. Is it doable? Realistic? If not, where could we still change/optimize something? If I forgot something, please let me know.

Thanks in advance for your feedback!

Hmm, equity is not necessary, just "desirable". We financed 100%, with one earner, not even a high income. The price for the house was 139k + 60k renovation loan. However, we had the purchase incidental costs in cash, but there was no real estate agent involved. Saving up - is it even worthwhile in the current low-interest phase? As I said, full financing is no longer a rarity today, no one gave us strange looks or asked why we have no equity (single earner, expensive rent, only earning for 4 years... what could one really save up?). If the bank agrees, why not? But I would pay attention to 2-3% repayment. We fixed it for 5 years - "back then" everyone said "how can you, interest rates can only go up" - well, they’ve fallen further and significantly! Good that we didn’t fix it for 10 or 15 years. Of the 5 years, 3 years are now over and after the 5 years we will have repaid 25k. However, there were also 2 special repayments included. We expect a significantly lower interest rate than the 2.5% (with full financing!) we are paying now.

If we took a forward loan now with utilization in 24 months, the interest rate would be a ridiculous 1.37% fixed for 10 years. So you don't have to be a prophet to say that it will be significantly cheaper.

If you want to finish repaying quickly, it is very important to have the highest possible repayment, especially at the beginning, because the saved interest and compound interest add up to tens of thousands of euros with a high remaining debt. Regarding the installment amount: our 100k component with 2.5% has an installment of 376 euros with 2% repayment. So 600 euros for 150k with 2% repayment should easily be feasible, the interest rates have fallen further. Better to take 3% repayment.

The question I ask myself is, who is buying the house?

You or you all?
If your girlfriend doesn't earn anything or not enough, how does she support herself?
If you are only counting on one salary, you still have to consider all the costs, and then your plan probably won't work.
In my opinion, you both should first settle into the working world. Then you will also know what you can afford.
At the moment, the whole thing sounds a bit like your dream and not your dream.

Of course, we are buying the house together - we agree on that. It may be that my motivation to buy a house is somewhat greater, but that surely also has to do with the fact that I am the one in the household who "oversees" the finances a bit and has more of an overview. My girlfriend hasn't been working for that long yet, that's true, but I have firmly settled into working life alone over the past 7 years with my employer. Because of that, I am very secure in my job. Even though she hasn't been working long, the job is also comparatively secure because in forensic psychiatric care they closely monitor who does the job and turnover is very low. Perhaps the basic statement about my girlfriend's income also got a bit lost. Over the next 5 years she is undergoing a correspondingly expensive further qualification and therefore cannot contribute more during these years than she currently does. Of course, the money is enough to pay rent, insurance, car, and so on. But during that period there is no room to save like I do. That means in effect the plan would be that I go in "advance" with my saved money and she pays correspondingly more after the 5 years or balances the whole thing out through additional repayments on her part. The only question is whether the plan with the above-mentioned key points can actually work. Oh yes, I deliberately only used one salary for the calculation because, despite the current circumstances and secure jobs, there can always be a loss, for example due to illness. And then I don't want to give the house directly back to the bank.

Everything may be true. However, the bank is interested in the total income and total expenses, not just your part, since both of you are listed in the loan agreement. My wife is also 5 years younger and studied. Since I did not study and have done a lot through part-time further training, I have almost a 10-year lead in working life. When she finished, we paid back the BAföG within a few years, got married, built equity, and then together we looked at where the salary journey was heading and what we could really afford. At that point, it no longer is about MINE and YOURS, but only OURS.

That may be true, but unfortunately it doesn't really help me with my question above. Everyone has their own life plan. Of course, such an investment must be approached together, nevertheless we both agree that, for example, it is not good if there is only one big WE/US lump. Everyone needs their piece of individuality. But that's a completely different topic - let's get back to the original post. So if we assume that only my salary + my girlfriend's previous rent payment (which is just under 400 euros) are available for financing. Would that be feasible? And above all: given the current circumstances, is it realistic to raise the missing 15,000€ within this short period?