Harvey pitched 26.2 innings in the Mets' first postseason appearance since 2006, going 2-0 with a 3.04 ERA and a 3.10 FIP. He was the center of controversy when he appeared to talk his way back into pitching the ninth inning in Game 5 of the World Series at Citi Field. Harvey had already thrown more than 100 pitches when he rushed out to throw the ninth, promptly walking Lorenzo Cain and giving up a one-run double to Eric Hosmer. Collins then replaced Harvey with Jeurys Familia. Hosmer eventually scored to tie the game, and the Royals went on to win the game—and the series—in the 12th inning.
Harvey pitched 189.1 innings in 2015 after coming back from Tommy John surgery, posting a 3.71 ERA and 3.05 FIP. His 4.4 fWAR was the tenth-best mark among NL starting pitchers. His agent, Scott Boras, ruffled feathers in early September by suggesting that Harvey should be limited to 180 innings. Including postseason work, Harvey surpassed that figure by 36 innings.