In A2A combat 5th gen fighters hold considerable advantage over 4th and 4++ gen fightets in most scenarios.
As to the Mig-25 versus F-15, there was no instance when a Mig-25 defeated an F-15 in 1990 (Gulf War 1?). What an Iraqi Mig-25 shot down by ambush was an F-18C. On the contrary 2 Mig-25s...