The result: A can shrink from 85 GB down to anywhere between 18 GB to 35 GB , depending on which content (campaign, multiplayer, zombies) is included.
Downloading game files from non-official sources, especially those labeled "highly compressed," carries severe risks: Highly Compressed & Cracked Games Ruined My Childhood call of duty black ops 3 highly compressed pc game
Some gamers use compressed repacks as “demos” to see if their PC can run the game smoothly before purchasing the legitimate version. Call of Duty: Black Ops 3 Highly Compressed