THE F 15 can reach mach 2.5 with a complement of air to air missles but otherwise, clean. Few missions require a fighter to excercise its top speeds. The F15 c’s on alert at Langley AFB would exceed mach 2 on some intercepts but generally not 2.5. The Eagles rapid acceleration makes it easy to go mach 2+. However, after a paint job there was a “burn-on” mission for a real hard paint which could be cured by the heat resulting from mach 2.5 and slightly over. It was done for that. That was the only mission I am aware of where 2.5+ was called for…not sure if they are still using that paint anymore… That paint was very, very durable, but extremely hard to strip off from a maintenance standpoint, it took lots of extra work.