You seem to know about this. Am I risking anything driving my 6 year okd old winter tires for 3 years non stop (winter and summer, 15k km yearly)?

There have been multiple fatal crashes caused by old tires on high performance vehicles. Notably, Paul Walker[0] died in a Porsche Carrera GT crash.

[0] https://en.wikipedia.org/wiki/Paul_Walker#Death_and_legal_re...

When buying new tires it's also very important to check date of manufacture. A tire can look completely new but been on the shelf for 3 years. tires deteriorate/age over time particularly when exposed to direct light. Tire warranty typically expires at 6 years from purchase.

For any sort of performance or classic car, good tires are paramount, you are literally entrusting the car and your safety to the road contact and adhesion of each tire.

US dot tire age location: https://www.tirebuyer.com/education/how-to-determine-the-age...

I agree you should change your tires and rubber hoses and parts which naturally degrade and rot but to suggest you have to have regular engine maintenance from it just sitting there (and by sitting i mean starting it from time to time and having proper cleaning but not actually driving) is pretty poor design. You shouldn't have to replace a transmission or mechanical part from lack of use. That is just an expensive form of planned obsolescence

Exactly. A different set of goals and compromises is what defines these cars.