He left DCR after the season ended because of their limited budget for a full-time campaign, and sought employment with another team for the 2015 season, saying: "It’s one of those things, where I could find out tomorrow, or it could be in another month or two months." Talks with Andretti Autosport owner Michael Andretti, who was interested in Wilson, about a full-time campaign ended in March 2015 over sponsorship issues. That same month, Wilson signed a two-race contract to drive Andretti Autosport's No. 25 car in May's Grand Prix of Indianapolis and the Indianapolis 500. He started his final Indianapolis 500 from sixth position. During the race a tyre vibration and a pit stop strategy error left him in 21st. Afterwards, Wilson obtained sponsorship to drive the season's final five races for Andretti, finishing a year-high second in the Honda Indy 200 at Mid-Ohio, in an aerodynamically inefficient car.