No, that's real bad mileage. I get 20 mpg with my 88 V6 4Runner and 23 mpg on the highway. If your O2 is reading rich then the computer is adding too much fuel. You need to find out why. I would guess there is a vacuum leak somewhere making the computer think it's running lean and therefore adding fuel. Check the intake rubber hose for any hidden cracks. Clean the throttle body really good. Check to see if the catalytic convertor is getting clogged or damaged. The automatic trans won't get as good of gas mileage as the 5 speed but you should be getting closer to 17-19 mpg.