I lowered my car 35 mm with a Sachs sport suspension kit (sold by Audi in Switzerland), but I still have a stock 15" tires. Handling was greatly improved, but those stock tires are not on a same level as my suspension.

What's your recommendation for tire size?
I have considered original 16" 5 spoke sport rims/tires or aftermarket 17" rims but I am not sure if they are too harsh for a rough surface. Also how big difference there is between 15" and 16" / 17" tires, what comes to handling and ride quality?