Thanks to ypg, Saruss, Bauexperte, and BeHaElJa, HilfeHilfe for your answers.
We have both been working since we finished school (studying alongside work and attending evening high school) and have never taken expensive vacations (once a year within Germany) nor spent a lot of money on fun over the weekends. The equity has been accumulated little by little. We currently do not have children.
We pay net rent of 450 EUR and are currently saving about 1500 EUR/month. If 45% of the salary is lost, then the 55% due to the tax class would be a bit more. According to my calculation, it would work with a payment of 1100 EUR, but then almost nothing remains for saving.
We had just known for a long time "where we wanted to go"
That is also the case for us. From the beginning, we knew that we wanted to consciously save our savings for the home. It is up to each person what is important to them in life, but we have decided it this way for ourselves. If we only had a third of the equity, we would probably build smaller too. Small, nice – but mine.