You key issue should be execution. At 15 cents/contract they must have some payment for order flow (no issue to you) or must have a smart router that will hurt your best execution. A lot of exchanges (especially the ISE - the most liquid) have maker/taker fees. If you are trying to pay bid/offer they may not route your order there. You could find that your executions are delayed or not happening as they try to source liquidity on an exchange that is free. If execution is an issue for you, you should investigate these guys more. If it's not, then the price seems great.
Apparently, a big market making options house owns this firm. I bet they are routing all their orders to their own market making desk and they are trading against their customers. they charge you 15 cents, but take the other side of your trades and hopefully make a dollar or 2 a contract. nothing wrong with this. ib does it also; which is why their smart order router is cheaper than directed execution.
Let me give you an example which will help you decide your broker. In my Fidelity account I put an order to sell 9 naked PUT for SPY 132 at 0.45. The bid/ask was 0.4/0.41 when I put the order. Then after 15 minutes one contract went through. Then I put the same order in my IB account for only one contract. That order (in my IB account ) went through but I still had 8 contracts unfilled in Fidelity. When the bid/ask jumped to 0.45/0.46, my Fidelity order was also filled !! I pay 0.71 per contract in IB ($1 minimum) and I paid about $16 in Fidelity for 9 contracts. Now which broker is better? If you ask me , I would say go with IB.
optionsxpress is probably the best for beginner option traders, top notch customer support and easy to use web gui. interactive broker is the cheapest by far and most flexible in term of what you can trade, but it's not beginner friendly you are basically on your own. Search for some of the IB liquidation engine threads. I would start with optionsxpress once you get familiar with everything for 6 months, move on to IB.