I think that those mpg's are achievable ....reduce the vol. of gas in the tank to 2 or 3 gallons, throw out all four seats the spare tire and anything else heavy, shove a skinny jockey behind the wheel, and set him off down a hill.
The reality is that it will probably be in the very low teens around town if you are lucky and mid to high teens on the highway without going crazy with the right foot.