The 2015 SummerSlam was the 28th annual SummerSlam professional wrestling pay-per-view (PPV) and livestreaming event produced by WWE. It took place on August 23, 2015, at the Barclays Center in Brooklyn, New York and would be the first of four consecutive SummerSlam events to take place at the arena. It was the first SummerSlam since 2008 to be held outside of Los Angeles as its Staples Center was the exclusive home for SummerSlam from 2009 to 2014. It was also the eighth SummerSlam to be held in the New York metropolitan area. The Izod Center in East Rutherford, New Jersey was originally supposed to host SummerSlam, but due to its closure in April 2015, the event was relocated. It was also the first SummerSlam to be four hours in length, a length previously reserved only for WrestleMania. This was also the last SummerSlam held before the reintroduction of the brand extension in July 2016.

The event was the second night of what was billed as a "triple-header" at the Barclays Center, with NXT TakeOver: Brooklyn having taken place the previous night, and Raw the following night. Ten matches were contested at the event, with no match on the pre-show. In the main event, The Undertaker defeated Brock Lesnar in controversial fashion; Lesnar put Undertaker in his Kimura lock and the timekeeper rang the bell after seeing the Undertaker tap out, but since the referee did not see Undertaker submit, the match continued. The confusion allowed Undertaker to surprise Lesnar with a low blow before trapping him in the Hell's Gate submission hold, which caused Lesnar to pass out, giving Undertaker the win.