Just out of interest, why the exhaust?
My first need for a turn down exhaust was when I added TorkLift tie downs for a cabover camper. The stock exhaust basically was virtually in the way of the tie downs. And it did put black diesel exhaust on the camper and the tie down. So.......I went with a turn down exhaust. And I liked it not just for fixing the soot problem and the tie down too close issue, but also for how it looks and how it works. Just because a 2015 is clean burning and the exhaust will not soot up the trailer or camper doesn't mean that I necessarily like the way the stock exhaust tip looks. Turn down just looks better especially on a dually with mud flaps. Perhaps a turn down would not look quite as "natural it just fits right and belongs there" on a single rear wheel truck.