I just got my first tank of e15 in my 2015 2500, and mileage is on par with premium 93 octane. The pump said it was e15 + 88 for flex fuel vehicles only. I do a lot of city driving and get about 15mpg with 93, 13mpg with 87, and 10mpg with e85. So far I'm holding 14.5mpg with the e15 and it's a hell of a lot cheaper than 93. It's a little more expensive than e85, but was 10 cents cheaper than 87. We'll see how the truck runs after this tank, then I decide whether or not to use e15 full time. It sure is nice being able to pick and choose which fuel to use.