Runtime is dependent on a number of factors so you just can't say you should get X minutes with a 4s 5000 pack. The 2200 Castle motor is based off a Neu 1515 1y. A very good and powerful motor, but it ain't the most efficient from a runtime perspective. The Neu version of that motor pulls about 120 amps. Also, racing will always yield less runtime than bashing around.
I think you will be hard pressed to make a 15 minute main with a 4s 5000 pack and that motor. You will probably need to get a 4s 6000 pack.
Track size, gearing, and driving style also play a part. However, I have found that motor choice and voltage are the primary determinant as to how long of run time you get.
With a 4s 5000 pack I could make a 15 minute main consistently with warm up laps and a 1512 2.5d motor on a very large track. That motor only pulls about 78amps or so, so it is quite a bit more efficient than the version you have.
Generally speaking, if you want 15 minutes consistently, go with a higher voltage pack 5s or 6s and a lower KV motor. I run 15 minute mains with a 1700kv Neu and a 5s 4350 or the zippy 5s 4000 pack.