Help on buying inFAMOUS 2, 15 GB!?

I really want to buy the game, but right now I can't go out to Future Shop to buy it, because it's about a 45 minute drive. Anyways, I saw that I could get the trial and then the game, but once I get the trial, then the game, will I have 15 GB permanently wiped from my hardrive. And if I get the game at retailers and not online, how much GB will it take up. This is VERY frustrating.