Outstanding Debt Protection in 15 Years

I know that he can no longer repay. I just wanted to say that I also believe that the financing model he chose is the wrong one.

I think you have a misconception there.

No, you are the one with the misconception.
Assuming he repays (if he could) 500€ more. Savings in the first month 0.75%/12=0.31€
versus
Deposit 500€ in a daily allowance account. Interest rate e.g. 1% in the first month 1.00%/12=0.42€

This results in an additional 790€ interest after 10 years compared to the interest savings if the repayment were made directly.

With consistency, some effort, and skill, and without much risk, the credit interest even beats the loan interest rate and is finished faster than with a higher initial repayment.

According to the profile, the OP is a graduate business economist. One should be able to assume commercial expertise.

!Attention personal opinion!

If the calculation is to work out, he must beat the loan interest rate or, strictly speaking, with the combination of the loan and his own savings, the alternative credit model (which we do not know). However, the OP suggested a building savings contract with 0.1% credit interest and a higher loan interest rate than the existing loan ... [ ]

And one should - in my humble opinion - think about that beforehand.

Best regards
Dirk Grafe

!End personal opinion!

It will "pop" in some form, either softened with a quick recovery like in 2008/2009, which I consider more likely, or more severely. Germany and the Scandinavian countries (except Iceland) are still the only countries in Europe with a stable economy and reasonably healthy financial markets, but even here there are already enough indicators that this will not last.

With a renewed note on personal opinion:

As you can see, this quickly leads to a fundamental discussion – and precisely for this reason, my mortgage financing is staggered or "pieced together" from several products. This has already proven effective, as I can react (almost) at any time.

Only 4.5 years have passed since my financing, yet one would structure it completely differently today. Nevertheless, I would always split (terms) and include special repayments. For my special repayments, for example, I can decide whether my monthly rate decreases or the term is adjusted when I make a special repayment. If I keep my rate, the repayment rate automatically increases.

In my opinion, financing with a single product is a gamble on a very specific development over 15 years. Instead, I would have "secured" at most half of the amount with this constellation and built the rest flexibly, possibly also immediately with suitable savings plans.

The current interest rates, for example, for overnight money compared to a fixed loan contract, do not reflect the individual risk either. Ok, up to 100K€ there is deposit insurance, but if you actually want to beat the loan with significant profit, only stock savings plans or similar remain.

Last but not least:

A (healthy) loan interest rate between 5 and 8% is, in my opinion, significantly more likely in 15 years than one at the current level. That means I expect a loan interest saving of at least 4%. However, I can currently only get an investment with a guaranteed interest rate of max 2%.

This is a scenario that, in my opinion, breaks your back and actually happened to some people in the 80s/90s. In the worst case, you save now for about 10 years at a level of 1-2% against the loan, where almost nothing is repaid. Then the interest rates rise; you do get high interest on your (small, because poorly interest-bearing for a long time) capital, but you also have to refinance the amount of over 200K€ minus the savings at the then valid conditions.

I think that would be bad for you. It would be better if the refinancing happens at the same level and you then repay more intensively.

Best regards
Dirk Grafe

With a renewed reference to private opinion:
....

Last but not least:

This is a scenario that, in my opinion, breaks your neck and indeed happened to some people in the 80s/90s. In the worst case, you are now saving for about 10 years at a level of 1-2% against the loan, where almost nothing is being repaid. Then interest rates rise, you do get high interest on your (small, because poorly interest-bearing for a long time) capital, but you also have to pay interest on the amount of +200,000€ minus the savings at the then applicable conditions.

Best regards
Dirk Grafe

Uh... Just the opposite – this "breaking your neck" is precisely what the building savings contract is supposed to prevent. I actually assumed that a building savings contract is a product understandable to everyone. But gladly once more slowly: I precisely do not have to pay interest retroactively at the then applicable conditions, since I could already fix the conditions (1.25%) now.