I was the same way. Could hardly get 15.5 and felt like I had been on dead empty for 2 days.
Learned a trick though- find a station with a pump that is on a slight decline towards your passenger side, like your right tires are on a downhill slope (luckily I have one at a Shell next to my office).
Once the pump automatically shuts off, top it off by holding the gas pump handle manually so that the gas is coming out at about half the rate it does when set on auto.
I do this and can usually get another 2 gallons in. Think it has to do with 1.) the angle the neck enters the tank allows for more fuel and less air than if it were on a level surface and 2.) letting the gas run at about half the rate decreases the bubbles that come up the neck and lead to an early shut off.
Works every time for me and haven't had gas come spewing out the neck yet.