Hey everyone, I have an interesting anecdotal report here on the difference between the 2013 and the 2015.
I frequently drive from Boston up to the White Mountains to go hiking. I also recently traded up from a 2013 C-Max to a 2015 C-Max. I did so this past weekend, with some interesting results. The trip, overall, was about 290 miles, and involved 80-90% highway driving, mainly at speeds of 60-70. I made this exact same trip several times last year in my 2013.
In the 2013 C-Max, I never got better than 44mpg on the round trip, and was usually in the 42.5-43mpg range.
In the 2015 C-Max, the trip this weekend ended at 50mpg for the trip (I made a similar trip earlier this year which resulted in 46.5mpg, but that was with only 400 miles on the car - I now have 2700 miles).
Needless to say, I'm quite impressed with the changes made between the 2013 and the 2015. Every tank since I got the car has been a 600+ mile tank and I haven't drained it empty (except the first tank; the car wasn't topped off at the dealer).
Just thought I'd share!