Exactly. As long as you watch the brake rotor and caliper size, you could be able to run a 15" diameter. Most of our pro-street / touring hybrids run a 12.19 dynalite rotor front and back. They normally run a 26" diameter front tire and a massive 31-33" diameter rear. Being that the brake rotors are the same diamter but the rotating mass of each (front and rear) tire is different, it eliminates the need for a proportioning valve. The 12.19 rotor up front is stopping a 26" tire where the rear 12.19 rotor is stopping a much larger 33" tire. Natually there will be more stopping force on the front.
BUT.... you may encounter that some 15" wheels may not clear the 12.19's calipers. That will need more looking into.
