If it keeps doing it take it back to dealer and tell them. It could have been an issue with the reflash. Part of the reflash was for the emissions, and it could be causing yours to regen more than it should. After the reflash my miles per gallon went up for about 2 months, then I started getting a lot of regens like you, and some lasted for over 15 minutes, and the MPG's went down. It then settled back down, but does regen more often which is because of the reflash. Dealer said if it gives me more trouble to bring it in and they will check it.