It’s a few min out of my way each direction to get to a gas station, then another few min to fill it up, sometimes longer if I have to wait. For some reason you assume that the typical fill up is what happens every time, for an accurate average you have to consider worst case scenarios too. I’ve had too many experiences traveling late at night looking for a gas station in a rural area only to be driving 30+ min out of my way to find stations that were either out of gas or closed. I’ve also had plenty of instances where there was a long line at the station for whatever reason. So overall it roughly rounds to 15.

Yes I was told to change oil every 3 months, I drive a lot. I had a ton of mechanical problems with my Lexus RX.