Well, after reading many previous threads here and understanding that many here on Escapist Forums have much to say on a the very sensitive subject of religion, let me offer my $.02.
I say let your conscious be your guide. If you feel in your heart, not because someone said so or what society says, but really listen to your own individial heart and soul and feel that this is an obstacle in your faith or walk with God, then perhaps you need to examine your feelings more closely.
Assuming you have a religious background and want to continue in your faith (and I'm guessing Catholic because you said priest as opposed to pastor/mentor/rabbi, etc) I'm serious in saying this is between your heart and God. If you can play a video game and are able to seperate yourself from it at the end of the day, and feel comfortable with your walk with God, then perhaps it's okay.
Religious or not, if you feel addicted to a game or it begins to be a controlling force in your life, maybe it's time to step away.
Now your focus is on violent video games. Myself, I am a 38 year old Christian and I admit I play GoW and CoD4. I feel secure in my walk with God/Christ, although some of the subject matter and swearing perhaps I'm a bit more sensitive to than others. I can't answer this for you, but if you feel that the viloence portrayed in any game distracts you, or takes your focus of of what you feel God has planned out for you, or somehow sits wrong with you, maybe you need to look into the reasons as to why?
The sheer fact you asked this question means you have a yellow flag within yourself that a certain game may not be sitting well with your growth.
Fish Food Carl and I are at extreme opposites when it comes to our belief systems, but I will agree with him that games in and of themselves don't turn you bad. It's how you interpet them and what you do outside. If they consume you and interfere with yoru walk, then..bad. I also agree with another here above...I'm not sure at first glance I want to know my pastor plays Grand Theft Auto IV, but then again I do, and I don't believe my ticket will be punched on that account. But then again, my calling is not that of being a priest.
Also, don't beat yourself up. You're 15 and your maturity is only beginning. Remember, true believers are not supposed to judge...that's a mortal trait, but only the Almighty has the authority and knowledge to know us inside and out. I don't think any of us here can truly answer with an certainity....listen to your conscious