Most CC processors will handle adult web sites now. The problem is - the set up costs (about $2,000). And this money goes to Visa/MasterCard. And then Visa/MasterCard wants around $500 a year to maintain records on you.
You still have to pay these high charges to IBill, CCBill, & and the other third party adult processors. This is one of the reasons why 2CO & Paypal do not accept adult websites.
Consider a real merchant account & you will not have to worry about the high discount rates. They still might be a bit higher than the norm (2.30-2.40%) - but should be a lot less than 15%.