I've heard of 225 fitting without a fender roll, but I don't know if anything far beyond 215 is a good idea on the stock wheels. If you are going to run a 225 tire, I think 225/55R15 is the closest match to the OEM rolling radius. I wouldn't recommend sticking with the current 215/65's, if you're going to keep that width 215/60 is a much closer match.

anthony