The only "safe" highly compressed versions of modern games come from trusted repackers like FitGirl (who have a legitimate website via .site domain), but even then, Black Ops 3 after installation. The magic 10GB version does not exist.
During Steam sales or on authorized key sites (like Humble Bundle), Call of Duty: Black Ops 3 often drops to or less for the base game. Zombies Chronicles edition is slightly more. Download Cod Black Ops 3 Highly Compressed Pc