Some sites claim to offer "Highly Compressed" versions of GTA 5 (e.g., 500MB) in CSO format.
If you are looking for the original, stable Rockstar experience on the platform, these are the only official titles available: gta 5 psp iso download top 19
To get the "GTA 5" look, tweak your PPSSPP settings: Some sites claim to offer "Highly Compressed" versions