A couple of things:
1. What blinds schedule are you using and what starting stacks? Hard to tell you how many chips to buy if we don't know how you are using them
2. NJ doesn't make $50 chips and even if they did, you probably don't need it in a tourney; just use 2 x $25. Things are easier this way.
3. For 10-15 players, 4 denoms is probably enough a 5th would mostly be useful for rebuys/addons which means at max 20 chips. See #1 above.
4. A 500 chip set might be tight for 15 players, see #1 above.
The CaptLego's calculator is a good start as is
this
article.
