If you want God of War III -style gameplay on a low-end system:

A PS2 cannot read PS3 code. A PS2 ISO is a disc image formatted for a 300 MHz processor and 32 MB of RAM. God of War 3 requires a 3.2 GHz processor and 256 MB of RAM. No amount of "compression" can bridge that gap.

If you still want to proceed, here are some general steps:

Let us cut straight to the chase:

God of War 3, released in 2010 for the PlayStation 2, is the concluding installment of the original God of War trilogy. It follows Kratos’ mythological battles to prevent the end of the world. The PS2 version, while graphically limited compared to the later PS3 release, remains a cherished entry for fans of the classic era.