The highest I have ever got was 15.6. I am about 60/40 city though. I understand that city driving is worse, but to be 3 mpgs worse, at my best, then what city is supposed to be rated at is a joke. My last tank I was at 13.1.
My "best 25" is 21.8 "best 50" is 20.1, "best 400" 15.1. 3500 miles and my mileage gets worse every single fill up, like I said my last tank was 13.1.
I also watch my mileage the whole time (and my fmaily thinks I'm nuts and laughs at me the whole time), and drive like a Grampappy. Coast when ever I can, and drive 65 (70 mph speed limit) on hwys, 45 (55mph) on country roads most of the time. I've never drove like this and it's starting to not be worth it, I wanna ripppp!!! lol