I don't run snow flaps on my sleds at all. They are needed ALOT less than people think.
My buddy's 15 xm with cut and trimmed flap has to constantly stop and cool with scratchers down and loose snow on the trail. My 14 with full flap never has to stop and cool on the same trails. (trails are a necessary evil)
I suspect it has more to do with cooler differences between between 14 and 15 (if there are any) but I'm skeptical about not running flaps at all as mine cools pretty well even in marginal snow. It also could be the brand of scratchers I suppose, but the eyeball test is what is: flaps=cooler trimmed flaps=not cooler.
I would love an expert but I can't fathom the skinny bars, shorter riser, and smaller seat. I'm 6'4" and 270 lbs, and I don't care what any pro says: Shorter risers are not "better" for me. They make my life miserable. Neither are skinny bars. Sticking with my '14 this next season.