Board Thread:News and Announcements/@comment-5503727-20151201031535

According to the 2015 manga sales, Nanatsu no Taizai lost to One Piece, but holds the next highest spot even defeating Attack on Titan sales (one of the most popular anime). It is the only other manga that sold at least 10 million copies this year.

http://www.crunchyroll.com/anime-news/2015/11/29/one-piece-dominates-2015-manga-sales-in-japan

I know the link discusses more on One Piece. 