Based on appearance/cosmetics alone... Hell yeah, they're small! (Particularly when they have a prominent lip) If the spokes of the wheel blend into the lip well (ie. Kosei K1 wheels), a 15" wheel will appear to be 16". Since I don't see a body kit listed in your mod list, 16's should suffice. Even better, ultra-lightweight 17's will do nicely. Unfortunately, ultra-lightweights are usually forged which means they cost a grip. (ie. SSR/Volks/etc.)
Personally, I would go with the 16" C8's. Are these Rotas by any chance!?