Martin’s publisher confirms that there is no new Game of Thrones (Song of Ice and Fire for the pedantic) book due for release in 2015.
I have to believe that the attraction of sitting in front of a desk writing all day has to fade once one’s real life catches up with his fantasy life. He is getting to run around with movie stars (and more importantly, starlets) and attending great parties. He is traveling in circles he did not formerly have access to, and has money to burn, so I imagine it is very difficult to marshal the discipline to lock oneself in a room and play make believe all day. And although his work can be of high quality, he was never greatly prolific to begin with.
I also get the impression that Martin is kind of irritated with how everyone keeps asking him about when he intends to finish. There is a video of him floating around on Youtube where he gives the finger to people who ask him if he is worried he will kick the bucket before the final book is published — typical socially awkward nerd response for the win!
About the only encouraging thing I have heard is that Martin saw the previews for the upcoming Star Wars trilogy and he remarked that it made him remember what it was like to be a fan and experience the anticipation of waiting for something to come out. He said it gave him new impetus to write and finish his own series. We will see how many words that impetus ultimately translates into being written. On the bright side, it is said that the producers of the TV show know how the books will end so that they can carry on should anything happen to George.
I imagine it is very difficult to rush that sort of work and the quality suffers greatly if one is not passionate about it.