15s dont fit 05+ GTs. unless you get the swaybar relocation kits for the rear. the brakes arent the problem, its the way ford mounted the sway bar, the end of it would interfere with anything smaller then a 16inch wheel. gearbanger is correct about that. so basically in order to run 15s you need to go to bmr or steeda and get the kit for the swaybar. imo not worth it to reweld brackets for your swaybars just to get a 1inch smaller wheel unless you are going for every last ounce of performance.