15's will be hard to get with what your putting together. My 3400lb 55 ran 15.3 at 95mph with 4 spd and 3.55 gears. The High gears you ae talking about will be hard to get the car going. Mine was really hard to get moving, I changed to 3.70 gears and changed to a holley 600 and its better. It is borderline though as far as being able to drive it on the highway. 4.56 would be the most I could run for performance but would be limited to being comfortable at about 50 mph on the street driving.