Dave,
Unfortunately, the Torq-Thrust wheels don't easily accommodate larger brakes. There's not enough caliper clearance. You'll have to change to a different wheel, like PS's.
12.18" rotors are the largest that will fit into 15" wheels, so if you're serious
, 17" wheels are preferable.
Alternately, better pads and calipers are available for the stock GM setup too. I don't have any experience with them, but I see a dual-piston floating caliper advertised in some of the Circle-track catalogs.