I'm getting tired of this. First, it was an exercise. Second, it was an exercise on Indian turf. Thirdly, the radar envelops were probably predetermined and radars not used in order not to reveal capabilities/emissions. Four, missiles were probably generic, for same reason. Five, it was a within visual range, no BVR scenario, the one the USAF is set up for. Six, was it in a 1vs1 scenario?exercise scenario might have predetermined the outcome, for example the F-15 is a red fighter attacking the bomber formation, the blue MiG-21 are protecting the formation. Could have been as crazy as 4vs1, because the goal is the blue fighter learn how to escort the bombers along the way. The F-15 just needs to try and shoot down as many bombers as it can. Or the MiG-21 was red force, attacking the formation is superior numbers to give the blue F-15 a hard time protecting the bombers. Seven, altitude? Eight, pilot experience? Nine, what else was thrown at the F-15, maybe it was doing SAM evasive maneuvers when the MiG-21 sneak up. Or it was chasing a Su-30.
In real life, the AWACS would have picked up the MiG-21 100 miles off, the F-15 would turn, pick it up on radar, fire one of two AMRAAMs at it, destroying it even before the MiG-21 comes anywhere close to enough range for its R-73. Break off and go after the next target or return to the formation, while the active missiles find their target. Do this in a joint exercise and It wouldn't be a good exercise for the MiG-21 pilot, he can basically take-off, take heading, enjoy the sound of its RWR bells while making one evasive turn, and then land, or do it again.