High Fuel Consumption Issues in My 2008 BMW X5 E70

I'm experiencing high fuel consumption issues with my 2008 BMW X5 E70. Over the past few months, my gas mileage has dropped significantly, from around 20-25mpg to a consistent 15-17mpg. I've noticed no changes in driving habits or road conditions, and I'm curious if anyone else has encountered this problem with their E70 model.