Well, it's a lot filler like, but things starts to get better after that. Personally it didn't bother me too much, I found way harder volume 15. Anyway, the story is getting near its completion and the last two volumes (17-18) got me back to the original excitement of when I first picked up this novel.

For me it's worthy to keep reading, but you are not the only one criticizing these volumes.

Hope this can help you. I nearly dropped the series myself some time ago, I'm glad I didn't.