I'm assuming you are talking 15+ with the ecobust? I had a loaner EB EL 4x2 with 3.73s for 22 days (while my '13 4x4 3.73 was in the shop). I can tell you I would HATE the 3.15s on the highway. The ecoboost in mild weather (only mid 80s and lower humidity) really ran out of steam past 80 mph. I can't think of how doggy it would be down here in the south when it's 99% humidity and 95 degrees. I wouldn't take anything less than the 3.73s or look at the lincoln if you don't need 4lo and go with 4.10s from the factory. The truck felt strong from about 15 mph to 60-70 depending on the heat and how long it had been stuck in traffic. I'm just not a fan of small displacement forced induction engines in 6,000 lb vehicles, they just don't work, never have never will.
As a note I've drive quite a few EB F-150s and they are very similar, they fall flat after the heat soak hits, something that doesn't occur with a large displacement V-8 these days.
