How PVPium ranks PvP IVs
For CP-capped leagues, PVPium searches valid IV and level combinations, then compares the resulting stat product. A high stat product usually means the Pokémon has more total battle bulk and can fit better under a 500, 1500, or 2500 CP limit.
The best IV spread is not always 15/15/15. Many Great League and Ultra League Pokémon prefer lower Attack IV because Attack raises CP faster than Defense or HP. Lower Attack can let the Pokémon reach a higher level while staying under the league cap.