Board Thread:Questions and Answers/@comment-95.42.252.90-20150303171841/@comment-6697950-20150303191436

Despite volume 15 being called "invading", it should actually end just before the invasion. The Alicization arc consists of two sub-arcs and volume 15 is just the beginning of the second sub-arc. It should go on for several more volumes, as the halfway point was in volume 13 or 14. However, the second sub-arc had a questionable ending and I've heard that it wasn't all too suitable for a worldwide release, so there is a chance that the author will change some parts of the story. Of course, it all depends on whether or not the author feels lazy. The ending for volume 13 hinted a very great deviation from the original plotline, but volume 14 returned it back on track, because the author couldn't get himself to write a different ending for it.

Oh, and it wasn't a forum. The author published the original story on his own website.

As for your last question, Alicization was the last arc in the web novel. But whether or not the author stops the series there are creates a new original arc is not yet announced.