Could it be you boosted the F-15 too much? I ran a couple of Ai-vs-AI missions today, cannons only, expert skill. The F-15 wins almost all the time because it outturns every other bird easily. Even when I put the F-15 in the worse position to start with. Only when I made Migs and Sukhojs significantly lighter they could actually keep up with the F-15's turning capability. Why did you do that?