One problem related to engine knocking noise has been reported for the 2015 Jeep Wrangler. The most recently reported issues are listed below.
Noticed significant knocking noise coming from engine that continued to get louder. Took to dealer for a nice 2 thousand dollar fix. Dealer replaced right side lifters, rocker arms, and both cam shafts. This sounds way too much like the 2011-2013 issue that Jeep "fixed" and was under warranty for those it sounds like. Very coincidental and I am not the only one with these issues based on Jeep forums.