If you are limited by data caps, look for reputable repackers (like FitGirl or DODI). Their versions are usually compressed to 2GB - 4GB , which is the limit of what is technically possible without removing core game files.

: Once installed, the game requires at least 8 GB of free hard drive space.

"Highly compressed" games are legitimate releases where repackers use advanced tools like 7z to shrink installer sizes. This is common practice. A typical highly compressed version of Assassin's Creed II is , which is a significant reduction from the final installed size of 5-6 GB.