It is impossible to put a 15" tire on a 17" rim. Do you mean you have a 17" tire on a 17" rim, or do you mean you have a 15"
tire on a 15" rim? You should not be experiencing any rubbing with the 15" set-up, but may with the 17". Go to the Classic section FAQ at the top of the section and find the tire and wheel charts to see if yours fits that car.