They'll do better than that on the highway.
My dad's Hemi Aspen gets 19 mpg on the highway and we got 11 mpg in his '07 2500 Hemi Ram towing my 8500 lb enclosed trailer.
You might get 14 mpg in town, but you should get over 20 mpg on the highway with a Hemi charger (unless it's an SRT8, then it will run mid 8's in the 1/8th stock)