I pull 8000-8100 loaded with the truck in my signature. The payload sticker came in at 2176 once I had the Lariat package and couple options. The truck has worked well pulling this trailer up, over and down grades in the Pacific Northwest. I have been very happy with how the 3.5L Ecoboost delivers power smoothly at lower RPMs. The integrated braking works very well. I have a good WDH / sway control and would advise you to do the same.
As for myself I would be hesitant to go over 8k loaded as you may exceed the hitch rating. Note 15% of 8000 is 1200, but I run more like 12.5% on the tongue. I have not seen the hitch rating for the 2015, but on my 2012 it is 1150. That means you can run out of hitch before you run out of payload.
One difference between my 2012 and the 2015 is the 2015 is 700 lbs lighter. A little less mass up front. I, personally, would be cautious about going over 8000 with a loaded TT.
Good luck,
Stu
