Wilwood does not make a BBK that will fit under 15" wheels sometimes the info obtained on the phone there is not correct.
I developed my own kit with 11.75" rotors and recently reworked it at a cost of $600 and a lot of time so others can work with a company I gave the info to and get this setup. I did not do this for making money just to help make it available and right now the only known 15x8 wheel that will work is the 6ul in 4x100 bolt pattern. With this setup the caliper is pulled in as far as possible which results in using around 11.5" of the rotor, there are no 11.5" rotors made that would work and 11" is simply to small for the weight of the car if one is going to seriously track it.
For 16" wheels which there is little available though the great Enkei RPF1 will fit this kit but not the standard 12.19" Wilwood kit, another 4x100 wheel.
Depending on mod level, power, suspension, etc, even the 12.19" BBK might not be enough for some ST's and at a minimum need brake cooling ducts.
Much lower weight wheels will help reduce the load on the brakes considerably, my street wheels and tires, 6ul on 15x8, 11.4 lbs each, NeoGen 205s, come in right at 31 lbs, around 11 lbs lower than stock, per corner, a huge performance gain in all ways except absolute grip but pretty close. My summer only tires, Konig Helix, 15x9, Rival S in 225, weight per corner around 32.5lbs, my race setup on the same wheels, 225 RA1 weight is around 31.5lbs.
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17's are simply to big for this car, 18's I will not even comment about, 16's are the sweet spot between real style and performance, 16x8 perfect under stock or if needed rolled fenders. There are some very good 16x7,8,9 wheels in the making, will be around 14lbs, cost around $159 each, flow formed so very strong, only in 4x100 which can be done for a very reasonable cost if do some looking into it, more so DIY as much as you can. No timeline yet as new molds have to be done, could be done, testing done, etc....the Wilwood 12.19" BBK likely will fit under them.
As always, lower weight rotational and unsprung mass has a huge effect on all aspects of performance, handling, braking, acceleration as well as ride comfort, usually noise and vibration, and wear and tare on the chassis.
Way too many new cars and some trucks have far to large a diameter wheels from the manfs, styling fad gotten out of control, just like far to much power in many cars, more than the car or drivers can safely use especially on public roads.