Full repayment or 15 years interest lock?

Just out of curiosity: What loan-to-value ratio are we talking about with that interest rate?

The interest rate for 40Y is certainly impressive. The question is whether that is really necessary. What about 30Y or even just 25Y, of course no longer full repayment borrowers, have you also received conditions for those? The remaining debt after the mentioned periods is also relatively manageable and if there is more money available at some point and a special repayment is made, the term shortens again

would be with 30 years or even just 25 years, of course no longer a full repayment loan

Full repayment loans often come with slightly better conditions than the same term with interest-only.

There might not be much difference, especially since the spread is only 0.58% with the offers at hand. But it would still be interesting for to inquire.

Recently, we were offered 2.39% for a module with 20 years as a full repayment loan (4% repayment rate); if we wanted the same 20 years with interest-only, e.g., 2.5% repayment rate, the interest rate would have been 2.79%...

The interest rates for a term of 25 years or 20 years with RS were not much better in terms of conditions, 20 years with RS was 0.4% better and 2% repayment, full repayment offered a 0.2% discount if you can put it that way

The loan-to-value ratio is 80%, 1 € more and the interest rate would have become significantly worse

which option would you prefer Advantages/Disadvantages

That depends on what expectations I have for my professional development, especially income development. If a rather increasing income (faster than inflation) is to be expected, I would choose the 15-year option.