If you can, please try to delete the Black Ops 2 game data folder.
For more information on how to do this, please see: Remove PS3 game data utility files
Also, try to use a soft cloth and wipe down the disc.
You mentioned the disc has scratches. Although they may not appear to your eye it's not an issue, the drive may have an issue reading the disc. Have you tried the disc on another console to see if the freezing occurs? This will help identify if it's disc related?
Additionally, a wired connection is preferred for online gaming.