for street use on an a15 you wont want a lightened fly, the a12 would be nice (if you have a flywheel from an a15 vanette now)

the a15 is like changing to a V8, super torquey and wont like revving hard (maybe it will but theres no point as the power is not up there)

you'll find yourself tootling along nice and quick just short shifting gears around 4000rpm, so dont spend any coin trying to improve high rev and dont put too big carbs on it