Sure, simulating extreme cases might be true, but those who swim in the middle field will be able to orient themselves. I will keep the 20 years interest rate mentioned above in mind.
You probably aren't allowed to post links here, but if you google a word, namely Bauzinsen, you get so many results that you could probably spend days looking, which is surely more effective than waiting for answers here from people who might have signed their contract a year ago...