This is what i wrote:
The F-15 was specifically built to counter the MiG-25 which they thought was an air-superiority fighter.
That does not necessarily imply that the F-15 program began before US intelligence found that the soviets were building the MiG-25. The USAF just changed their requirements.
The initial designs, not even functional prototypes, were rejected. We are talking about several HUNDREDS designs here. So if these hundreds PAPER designs were rejected, they must have been rejected before our intel discovery of the MIG-25. That mean the final accepted F-15 design happened at best roughly the same time as the intelligence discovery of the MIG-25, but more likely it was agreed upon before said discovery. In order for your argument that the F-15 was a 'response' to the MIG-25 to be valid, it must be established that the US must have been beyond the 50/50 certainty threshold of the MIG-25's capabilities. That was not the case. We did not know of the MIG-25's true capabilities until 1976 with Belenko's defection in a latest MIG-25 to Japan. Prior, the only thing we knew of the MIG-25 was its detected speed and by that time those hundreds of paper designs were already rejected.
As far as I know, there is no proof to state that the USAF changed their requirements before the discovery of the soviet project as the actual dates of the discovery and change of requirements is unknown. Here's something I found on wikipedia:
With a top speed of Mach 2.83+, a powerful radar and four air-to-air missiles, the MiG-25 worried Western observers and prompted development of the F-15 Eagle in late 1960s.
The MiG-25's huge tailplanes and vertical stabilizers (tail fins) hinted at a very maneuverable aircraft, which worried the Air Force that its performance might be better than its U.S. counterparts.
So you think that the US decided to just sit back? This percieved threat of an advanced air superiority fighter from the Soviet Union which may out-perform all USAF planes has surely gone into serious consideration while developing the F-15.
That mean the final accepted F-15 design happened at best roughly the same time as the intelligence discovery of the MIG-25, but more likely it was agreed upon before said discovery.
McDonnell Douglas' design was selected in December 1969, not 1967.
Then it is even the greater fool to speculate that the MIG-25, an 'interceptor', can be so skillfully exploited that the only thing the pilot need is greater speed to shoot down an F-15. That is like saying the bomber pilot can somehow position the fighter below so the falling bombs can destroy the fighter.
The MiG-25 is definitely at a great disadvantage. But it is not impossible for a MiG-25 to score a kill. Here are some possible strategies for a MiG-25:
1. Defensive strategy: When a MiG-25 fighter who knows the strengths and weaknesses of his fighter feels he is fighting a loosing fight, all he has to do is get low and accelerate to Mach 2.8. The F-15's may manage to get a lock and fire AIM-7 or AIM-9 missiles though these can be countered with active defences (chaff and flares). The F-15s cannot keep up with the MiG-25s and will be forced to give up the chase.
2. Offensive strategy: Here, the best strategy IMO will be lightning fast attacks (a strategy similar to the one used by the German Me-262 and the Me-163 in WW-II). The MiG-25s should fire their missiles before the Americans can get a visual ID and then accelerate to Mach 2.8 and get as low as possible. Any possible missiles fired by the Americans can be countered with active defences. The F-15s cannot hope to catch up to the MiG-25s and will be forced to give up.
A MiG-25 pilot should avoid turning fights at all costs.
The SR-71 does not need its engines removed after every mission and every mission was Mach 3+. In other words, destroying the engines is NOT normal. So when we say so-and-so aircraft's top speed is so-and-so knots per hour, we usually mean the aircraft is capable of repeating it WITH THE SAME ENGINES...!!!
The MiG-25's engines are capable of reaching Mach 3.2+ but the
MiG-25 was redlined at Mach 2.8. This is because at higher speeds, the engine would overheat causing damage as the engine was never intended or designed to be operated at those speeds. So, we usually say that the MiG-25's top speed is Mach 2.8.
The MiG-25 is designed to allow flight at Mach 2.8 without damaging the engine. The F-22 is also able of reaching speeds that exceed its design speed limits, particularly at low altitudes. So max-speed alerts have been included to help prevent the pilot from exceeding them.
The SR-71's engines are designed to be operated in afterburner continuously as opposed to conventional jet engines. In fact, the SR-71's engines become more efficient at higher speeds.
But the SR-71's engines had to be started by two V8 engines on a "start cart". 
