2 months ago, I got the same mpg as yours, but now it's winter time, they switched to winter gas and I drive short distance per day(10 km oneway), I am getting 16 mpg on city drive, and haven't driven too much on highway since winter came.
It's not very cold yet, I will feel lucky if I get 15 mpg in January.
99 BMW 540i 6-speed 110K Km
03 SAAB 9-5 wagon 80K Km
92 400E (Sold) 245K km
Still missing the days with the Benz, it kept me busy.