I've seen people fit them on 15's before after having a machine shop grind the caliper or wheel down a bit to clear them. I've never seen a 15 clear without modification, but maybe someone esle knows more than I. If the offset is the same as my old stock SE S14 wheels then the offset should be fine. The calipers for both the 26mm and teh 30mm should be the same thickness and should not affect the neccessary offset for the wheel. And as you said they are both 280mm in Diameter so it should be the same affect. GOOD LUCK!
