No. Sub based games thrive on people paying more than they play since they have no whales (nor should they) to keep them afloat.
Here's some ideas I came up with in another thread OP, that I *might* support.
1. Pay by allowing the game to access additional CPU resources while you play. Depending on how good your system is they can get a little extra computing power for cheaper then usual and you don't actually have to pay a direct fee (it'll be coming out of your electric bill later, though.)
2. Add *tons* of RARE vanity items to the in-game drop list and make an RMAH for just those vanity items. To boot ZOS can take a small tax out of every purchase.
3. Surveys and polls. I've seen a few F2P games try this and it usually ends up a spamfest but if conducted correctly I think letting players do a couple of surveys on the side if they opt into it and have this add credit to gametime every so often. It might not make the $15 all at once but over a few months you might make up enough to pay for an extra free month.
4. Optional client with advertisemants. The assets you generate from views and clicks would be displayed in your account info thing on the official site and however much you have left that you still need to pay would be deducted.