I personally owned a 2015 F-150 MaxTow 6.5' bed, Ecoboost 3.5L, etc. I towed my 8500lb dry 35' toy hauler home from the dealer (40 miles or so) and even with my WDH with sway control, etc. a few big rigs came next to me and pushed me all over the damn place. It was totally diff from pulling my smaller 4000lb trailer (which the 2015 F-150 did with ease).
Subsequently, I sold the 2015 F-150 and have a F-250 PowerStroke Diesel now (2012 6.7L)
BTW, MPG on my f-150 sucked. I got 12.5-14mpg on a normal tank driving to/from work. You never get that high mpg if you ever boost. I get better MPG with the diesel now.
Also, you wont have much luck finding Max Payload, since it requires a different frame (slightly beefed up) and some other items. Ford I am told pushed off Max Payloads till 2016 now.. The Max Tow of coruse.. but if you want to do Max Tow and MAx Payload, I would recommend an F-250. You will be much happier, *I* am. I lost thousands on the switch too :(
Here's my old window sticker - http://fordlabels.webview.biz/webviewhybrid/WindowSticker.aspx?vin=1FTFW1EG9FFA25165
