Sadler's first game after signing for the club on a permanent basis came in the opening game of the season, in a 2–1 loss against Millwall. A regular in the side in the early part of the season, Sadler scored his first goal for the club in a 2–1 defeat to Chesterfield, but lost his place in the first-team after a run of poor personal form. Having been recalled for an FA Cup first round victory at non-league Gainsborough Trinity, he was praised for his "first class attitude" and determination by manager Micky Mellon. Sadler later scored his second goal of the season on 26 April 2016, in a 2–1 loss against Walsall.