How to let my parents let me get Grand Theft Auto IV?

Hi I'm 15 going on 16 and I was wondering what to say to my parents to let me get GTA 4. I already have Red Dead Redepmtion and Fallout 3 and Mass Effect and several other games that have just as much objectional content. My parents are really religious and not to mention impressionable so when they saw on the news a while back they've been totally against it. I've tried to tell them that the games I already have are just as bad but my mom won't listen and says she's "totally against it". What should I say?