Since Mahrez became a full time player, his league goal totals have been:
13-14: 5 (split between Le Havre and Leicester)
15-16: 17 (but four on penalties so 13 npg)
16-17: 6 (three on penalties so 3 npg)
He isn't really a goalscorer, he's a tricky creative attacking midfielder who finds the net every once in a while. The 15-16 season was a massive massive outlier that he has never come close to replicating in any other professional season. Expecting him to replace Sanchez as the goal scoring wide forward in our team would be really foolish.