What you might get is a modded version of Grand Theft Auto: San Andreas (which is ~700MB when compressed). A modder has reskinned CJ to look like Niko, replaced radio stations, and renamed the map. It is not Liberty City. It is not GTA 4’s Euphoria physics engine. It is a skin-deep illusion.
No legitimate compression technology exists to reduce a 15 GB open-world game to 0.1 GB while keeping it playable.
: Some malicious files, such as the "Avenger AIO" virus found on shady sites, can permanently delete Windows Defender and require a full OS reinstallation to remove.