On April 15, 2015, Pinder made his major league debut against the Baltimore Orioles, going one inning and allowing one hit in a 7-5 loss. He was optioned to Triple-A on April 21 in exchange for Chasen Shreve. He was recalled on May 9 after Chris Martin was placed on the disabled list. He was sent back down on May 24 to make room for Jacob Lindgren. On June 19, Pinder was called up yet again after Martin was optioned to triple-A. On August 30, Pinder collected his first major league hit, an RBI double, off Atlanta Braves pitcher Jake Brigham. It would be the only at-bat of his career, giving him a career batting average of 1.000. He finished the 2015 season by making 25 relief appearances with an 0-2 record and a 2.93 ERA.