I find it funny that most everyone believes that 15's and 10s go together. A "best of both worlds" if you will. You get the low end of a 15 while getting the punch from the 10s. I used to think this was true too and thanks to people more knowledgeable than me on TB and a good friend that runs sound and plays bass I have learned differently.
I agree with the others. Running 10's and 15's can work, but it can also be disastrous. I vote to get one or the other.