Don't risk your computer’s health downloading suspicious files. Because the hardware architecture is fundamentally different, GTA 4 will never run on a PlayStation 2. If you want to experience the HD era of Grand Theft Auto, your best bet is a second-hand PS3, Xbox 360, or a modern PC.
If you just want to play GTA IV without buying a gaming PC or an Xbox:
: Rockstar Games released GTA IV only for PlayStation 3, Xbox 360, and PC. gta4 ps2 iso highly compressed repack
: Available via Steam or Rockstar Games Launcher (Complete Edition).
"Highly compressed" files (e.g., claiming to shrink 15GB to 500MB) often contain viruses, miners, or adware instead of real game data. If you just want to play GTA IV
The pursuit of a "gta4 ps2 iso highly compressed repack" is a trip into the world of internet myths. The PS2, while legendary, cannot run GTA 4. While fans have created impressive mods to make San Andreas look like its successor, it is not the true experience.
If you want, I can help with legal alternatives or related legitimate content such as: The pursuit of a "gta4 ps2 iso highly
If you want the console experience, playing the game on its original hardware is the best option.
The differences between what the PS2 could provide and what GTA 4 required explain why an authentic ISO file cannot exist: