GT15 and a T2 are one in the same thing, but the GT range of turbos have more efficient turbines. So better to just use a GT15.
unless you want to use the mirage kit, as doesnt the GT range use a difference exhaust downpipe flange; like the GT17?
Well as I remember Mirage now make manifolds for the GT range rather than the T2. Could be wrong though, they're not mentioned on his site.