$15 dollars a month is nothing.
Plus there's truly no such thing as a free MMO, at least not that I've found - 'free' MMOs have cash shop type stuff were those who pay good amounts of money (which can easily add up to more than $15 a month) get huge advantages, and those who don't are left behind. Even if you find a truly free MMO, the customer service would be no where near that of a paid game.