So, currently I'm 10th prestige on the last three CallofDutys, Cod4, WaW and MW2. I was wondering how long it would take me to get to 15th prestige on a new account.

Im fairly decent and Im a hardcore S& player. Averaging about 5k+ score a game.

Currently, Im a level 43 with 9 hours played. *I started playing BlackOps on Friday*

Let's do the math. You began Friday, roughly 3 days ago; if you have 9 hours, you average 3 hours daily. Let's just assume it will take you 3 more hours to hit rank 50 (making 12 hours). To reach 15 prestige level 50, you'll need to repeat this exactly 15 more times. Multiply the average sum of hours it takes you to reach level 50 by 15, and you get a result of 180 hours that you will need to reach your goal. In total, it will be 192 hours if your experience and hours of gameplay remain at a constant daily rate, meaning you will be 15th Prestige with just over 8 days played. There are approximately 730 hours in a month, it's up to you to determine how those hours will be disseminated.