Curious what brand 15" tires you are running. Seems like it isn't hard to find a 15" tire, but if you want one with a modern compound, they are few and far between.
Either way, it comes down to what you want to do with the car. I think much like building a "600 HP motor", we as a community get wrapped up in the idea of something when the reality is if we are realistic with what we build and accept it for what it is, we will be just as happy. If not more. I know I have done that with brakes, no reason I need 14.2" rotors and 4 piston Brembo calipers. But I still want them and plan to run them even though it forces me to 18" wheels and tires.