15lbs is not really important, at 14lbs you have the core and hit so I say don't worry about it after you are at 14. I would agree that at 130 there is no real need to buy A) a premium ball and B) a 5th ball if you are going to continue use of the rest. My suggestion, is grab a Blue Vibe, you can leave it in factory finish for a great all around ball, or sand it down just a bit to have a ball that is more aggressive than the Ebonite NV series up to this point.