I honestly don't know how you guys average more than 15 in city driving unless you have 30mph speedlimits and only 1 light/stop sign per 2 miles or so.

Here there is a stop light (or sign) every 1-2 blocks, speed limit is 40-45. On the freeway your lucky to get up faster than about 35-40 and generally it comes to a stand still every mile or so for onramps/offramps.

 

I usually hit reset on my odometer when I fill up... is there something else you need to do to clear the average?

 

Yes, reset it.