Like KingRat said, your rig is pitiful. I'm surprised you can run PCSX2 to be honest. If it is not your rig, then it is the game. PCSX2 has no problem emulating most PS2 games, but there are some games that it will simply not run. For example, Star Wars Battlefront 1 and Ratchet & Clank 1. You could degrade the graphics all you want but you'd be lucky if you got more than 10fps for Battlefront and 15fps for R&C.
Honestly, it would just be easier to purchase the game and console than deal with the frustration PCSX2 dishes out sometimes.