The back spacing on my Shelby Cragars is 4 1/8". Don't know what back spacing is on the Torq Thrusts. I currently use PSE 15 x 8's.
What really matters is the wheel offset (whether the center of the wheel is inward of outward of the hub flange). 15x7 TTD's for example have a 3.75" BS and since (almost all) wheels are ~1" wider than their "advertised" bead width, that means that the center of the wheel is 1/4" offset outwards relative to the hub.
The 15x6 Cragar wheels are 7" wide and with 4.125" BS, they are offset 5/8" inwards, relative to the hub. The tire center is therefore 1/4 + 5/8 = 7/8" more inwards.
In case of 15x8 PSE wheels with 4 3/8" BS, the wheel center is 1/8" offset outwards, relative to the hub (slightly more inward than the TTD's and consequently slightly more tire room)