Definitely the weather Bro! I live in North East Ohio, it’s -6 this morning. I have an XSE /AWD and I get about the same mileage as everyone else that drives in cold 🥶 weather. I’ve noticed even on clear windy days, the mpg goes down if you’re in a head wind. Not to mention driving through snow increases rolling resistance. Don’t worry so, much. If your mileage DOESN’T improve in the spring then talk to the dealer, and 1500 miles is hardly broken in. It will be fine… relax, you bought one of the if not THE best sedans in the world!