Got my 2015 GSW M6 done a week ago. I DO notice slightly less turbo lag off the line. Mine seemed to go into regen at some point daily, regardless of miles driven, for the first 3 or 4 days. I believe I had plenty of time on the road for the cycle to complete, so maybe this is a difference. I'm very happy to be keeping my wagon. After warranty/performance/restitution info came together, it seems the obvious choice for a 2015 owner, unless you don't like the car or you choose not to own a VW for awhile.
One thing I will say is that people saying things like, "I filled up the same day of the week", or "It took the usual amount of fuel", or "I got 500 miles on a full tank like usual" etc... PLEASE KNOW THAT NONE OF THAT IS AN INDICATION OF ANYTHING. YOUR THINKING IS COMPLETELY INVALID, AND YOUR ASSUMPTIONS AS TO THE MARGIN OF ERROR ARE ARBITRARY AT BEST. You might as well blindly throw darts at mpg numbers on a board. Seriously friends, it's a two-second grade school calculation. You could also pay $0 for any number of very simple car-related apps that will calculate for you and keep ALL THE VALUABLE AND NECESSARY INFORMATION that you WILL need to keep your car running properly. Instead of a mechanic ripping your car apart to evaluate it's condition, you can have all the answers in your pocket. It's tough for me to understand someone buying a new car and not keeping an accurate log of all fueling and maintenance.