Well even though I'll have 15" wheels, the overall tire diameter will be the same. This helps maintain spedo readings and gear ratios. I'm not sure they'll even sell you tires+wheels with a smaller diameter at most tire stores (I've heard of discount tire refusing to do this)

The question arises, then, that with this increased sidewall height - will the tire absorb more force and decrease the rigidity of handling? I know I could counteract this with increased pressures if needed.