Poor Gas Mileage Question

I have a 07 accord ex-l v6. now I know that the what they say on the sticker that the car will average it usually off but my car is averaging about 12-15 mpg normal driving. that's not even gettin on the throttle and using vtec. I went to the dealer and naturally the service writer said that that was normal, especially around the winter time. but I bought it in the summer, and I've noticed it gettin poor gas mileage since the beginning. Is this normal? If not what exactly could be causing this? Any help is appreciated. thanks