For 2015, Carpenter again shared the No. 20 Dallara-Chevrolet entry; he contested the oval races and Luca Filippi contested the non-oval races. Carpenter first competed at the Indianapolis 500. On the morning of Pole Day qualifying, Carpenter half-spun in turn 2 and the left side of the car hit the outside wall. The car flipped over and slid down the back straightaway. Carpenter was unhurt in the incident, but as a result of the incident and similar crashes earlier in the month, the series decided the reduce the boost on cars. During this time, Carpenter's team prepared his back-up car. Carpenter qualified 12th for the race, in which he struggled and was running in the top 15 when he attempted to pass Oriol Servià for position on lap 113. The two drivers made contact and crashed into the turn 1 wall and Carpenter was scored in 30th place. Carpenter then competed at the Firestone 600 at Texas; he started in 15th place and finished in 22nd place due to an engine failure after completing 147 laps. Two laps later, Carpenter's teammate Josef Newgarden also retired due to an engine failure. At the MAVTV 500 at Auto Club Speedway, Carpenter started in 4th place and was involved in a crash on the main straightaway with Newgarden on lap 158 and was scored in 22nd place. He then achieved finishes of tenth at Milwaukee, sixth at Iowa and seventeenth at Pocono. As a result, he finished 27th in points.