14 mph is probably average....based upon the way most drive.
I just wave when they blow by me at 70mph!!!
The delivery times are based upon 45 or 50 mph. There is no reason to drive at 70 mph...unless you are a Super Trucker.
My 2008 Aerocell with dual rear wheels and weighing about 2000 lbs more than a regular cargo van can get 14 mpg.
And my 2008 Chevrolet Express 3500 Ext WB can easily get 18 mpg.