Last Thursday, Kazu gave us a little "progress report" on the next book in the Amulet series via Twitter. He stated that he will be working "around the clock" for the next two months and that the book has been a challenge to produce. A few months ago, Kazu answered a fan's question and told us that the next book should be released around early 2016. Fortunately (or unfortunately), the year seems to be going by rapidly.
Looking at the picture of Kazu's work desk, it seems that he has made impressive progress on the new book. (Is that Max in one of the panels? I might be wrong.)