I'll offer you one comment. Be 100% sure of the tire you plan to run on the rear before you invest in 15's. What was common a few years back has become rare as hens teeth today, and the specialty tires from Coker have become of questionable quality. Bigs & littles refers to the diameters, not just width, and the "tradition" is to look for six to eight inches of rubber rake if you're going for the big & little stance. Based on your comment about the car that Randy posted and the wheel sizes you posted, I believe that your definition must differ.