A 10-15hp difference is just about within the margin of error for our cars. One run can be 350hp, the next can be 340hp without changing a thing. So, it's not likely that you'd be able to see such a small change unless you did a bunch of dyno runs then took the averages of the before and after...even then, there's no guarantee that you'd be able to notice a 15hp difference.
The best mod I've done to my car performance wise, so far, is the headers. I just went with the JBA shorties, so I suspect that going with full LTs would make an even larger difference. I didn't do a before and after dyno though. I did FEEL a difference on my butt dyno, however.

I do have the K&N CAI, and honestly, I didn't feel much difference. Honestly, I think you're be just as well off to slap a regular K&N filter in your airbox and be done with it, that way you won't have to worry about heatsoak...much.