I went with 15 - 16 also because that IS what I get around town... About 15 in the summer with the A/C blowing and about 15.5 in the winter.... Don't know the highway mileage because the only longer trips I take are pulling the 5th wheel (at about 18,000 - 19,000 lbs gross combined)... When towing the worst I've gotten is 12.9 and that had it's share of uphill at 60 and 65 mph so I'm not complaining....
Ken....