He was retained by Porsche for the 2015 season and again raced with Bernhard and Hartley in the renumbered No. 17 car. Webber and Hartley qualified their 919 Hybrid on pole position for the season-opening 6 Hours of Silverstone but Webber was forced to retire the car early in the race with drivetrain failure. He was on pole position at the following 6 Hours of Spa-Francorchamps and finished third after Hartley incurred a stop-and-go penalty for rejoining the track via an escape road. His team qualified second at the 24 Hours of Le Mans and finished the race in the same position after Hartley was observed speeding in a slow zone and Webber served the subsequent one-minute stop-and-go penalty. He and his co-drivers went on to claim four consecutive victories in the following four races to enter the season-ending 6 Hours of Bahrain leading by 12 points over Audi's consistent trio of Marcel Fässler, André Lotterer and Benoît Tréluyer in second position. Webber and his teammates needed to finish third in the race and for Fässler, Lotterer and Tréluyer to win in order to clinch the World Endurance Drivers' Championship. They qualified on pole position and came through mechanical problems for a fifth-place finish and title victory with 166 points, five ahead of Fässler, Lotterer and Tréluyer.