One problem related to gas recirculation valve (egr valve) has been reported for the 2015 Ford Mustang. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2015 Ford Mustang based on all problems reported for the 2015 Mustang.
Upon approaching a red light with the clutch pedal pressed down, and manual trans in neutral the engine died. Also had "run power on" on the dash. Bumped the start button and it started right up. Description of electrical issues: temps outside were mid 80's. (car was still cold engine wise and I had the a/c on full blast when it died. ) dash board information/touch screen readout said it was 70 degrees outside while temps were in the mid 80's. And as I was driving, (city traffic) I would shift at or around 2500 rpm. When I pressed in the clutch to shift the rpm's would jump about 1000 rpm's until I let the clutch out. This occurred about three or four times out of ten to fifteen shifts. About 3 miles up the road I pulled over, shut the car off and opened the door to turn off the stereo and touch screen. Cranked it up and right away the outside temp reading was the actual 85 degrees. No more revs on shift and ran fine all the way home for the next 15 miles. Reporting this due to multiple issues of this being reported by other 2015 Mustang owners on social media and Mustang related websites.