The F-15 was specified to have a maximum speed of Mach 2.5. However, I believe this was reached only once during Developmental Test and Evaluation and they had to change the engines afterwards. On the production models, there was an overheat switch in order to get to this speed, but the A model only had 11,300 lbs of gas so having this capability was a joke. And the switch had a wire the pilot had to break to throw it. All supersonic aircraft with the exception of the SR-71, the F-111 and Soviet MiG-25 did not have enough gas to make top speed usable. People forget the three main parts of fighter aircraft performance, thrust to weight ratio, wing loading, but equally important is its fuel fraction. Most jet fighters have fuel fractions between 25% to 30%, that is, at takeoff gross weight you divide that into how much internal fuel the fighter can carry and you get the fuel fraction. Why is this important? Well the fuel fraction tells you how far you can fly or stay in air combat and return. In the case of the F-111 it had a fuel fraction of 38% so it could stay supersonic for awhile. The surprising thing about the MiG-25 is that its fuel fraction is only 26% while the SR-71 fuel fraction is 56%. The MiG-31 has a fuel fraction of 47%. The other part of this is how fast the engine burns fuel measured in Thrust specific fuel consumption, that is,how much fuel does the engine need to produce the required thrust for a given altitude and speed condtion.