X5 35d -- first tank, really bad mpg?

I am about 1/2 through my first tank on a new 2012 X5d and, after about 90% true city driving (Chicago), the trip computer is showing about 15.7 mpg. I am not hitting it hard or anything, just a ton of stop-and-go traffic (and yes, I reset the trip computer before I left the dealership). Is this normal or does it get better over time? I am most interested to hear from X5d owners who do mostly city driving. Thanks in advance!