I'm getting 14 mpg if I stay off the pedal. My 2008 Toyota Highlander was getting 16. And my wife's 2010 Honda Minivan gets 18. All in town driving.
It was easier when everyone was at home because I could drive to time the lights. Now I get people in front of me stopping and people behind me mad if I don't go faster.
If I wanted gas mileage, I'd drive the mini cooper to work. ~28 mpg and a 12 gallon tank.
You're putting on 1,500 miles every couple weeks? I put on 3,000 in a year and a half going back and forth to work. You'll need something that gets 40 mpg or better to save any money. I'm selling the mini, because better gas mileage doesn't cover the added taxes and insurance expenses. I doubt you'll save money with a second car in the long run. Especially if you borrow any money to buy it.