On August 2, 2015, Porcello was placed on the Disabled List (retroactive to July 30) for the first time in his career, with the Red Sox stating he was suffering from triceps soreness and inflammation. At the time, Rick was mired in his worst season, statistically, having posted a 5–11 record and a 5.81 ERA prior to the injury. He returned August 26 and threw seven shutout innings in a 3–0 win over the Chicago White Sox. In his next start, September 1 against the New York Yankees, Porcello struck out a career-high 13 batters in 8 innings, but lost a 3-1 decision. Porcello finished his first season in Boston with a 9–15 record in 28 starts, and an ERA of 4.92 which tied his career high. He gave up a career-high 25 home runs, but also had a career-high strikeout rate (7.8 K/9).