Besides �for what crazy motive Peru will need Mig-25 (Mig-31)?This is and advance, long range, supersonic aircraft intended for interceptions of long range intercontinental Bombers, among its weapons are long range air to air missiles, similar to de Phoenix class american missiles, with ranges of 100 miles, suitable for BVR (Beyond Visual Range)
There is no actual treat of intercontinental Bombers in Southamerica, plus the geographic environment of the Andean region dictates that the required platform of choice will be of a total different kind, and not a Supersonic, Heavy punch, less maneuvrable juggernaut like the Mig-25 (Mig-31).
Its simply to much for the nesecities of the Peruvian Airforce.
Picture Link
Bomber Killer