If you put a Nitto NT01 R compound next to a Hoosier Rcompound 225 45 15 you will see almost an inch of difference in width (its crazy) thus I would NOT suggest you try to stuff a 225 45 15 Hoosier R7 or older R6 on a 6.5" wheel. I've done it myself with a NT01 (it gets a little silly looking but it can be done)
Something to keep in mind, you really won't gain that much more contact patch because of the rounding (you really need wider wheels to get the full contact patch gain of wider tires)
If it were me, I'd stick to 205 50 15s on a 6.5" wide wheel because you just won't feel or notice the benefits of a 225 on a 6.5" wide wheel.