It is a challenge to find good 15" tires for Cobras (that's why some folks go to a 17" rim, as it's much easier to find 17" performance tires).
For 15" tires, as already mentioned, some go the drag radial route.
Others like the Goodyear Billboards (the downside is that they are bias ply, but they have the nice vintage look to them, and traction is supposed to be pretty good).
Another option to consider is the V-rated Avon radials (see attached link for a thread on the Avons).
Mounted the Avons on my SPF
I have a pair of Billboards and Avons on order.