There is a button in admin to delete all hidden posts so you could do that on occasion.
For me, the total size of my database with 3 Q2A installations, thousands of questions and answers and comments, plus the tables for my regular site, all total 300 MB. So I really doubt it's anything you need to worry about.
Note that I am not storing user avatars in the database as I use Gravatar, so if you are doing that it may fill up faster but I doubt you'd get close to 2.5 GB. If you do, you are probably doing well enough to be able to afford better hosting ;)