First I’d answer the question: should there be any gas stations at all? With self driving vehicles you could imagine a future where self driving gas dispensing trucks roam the highways to refill cars as they go.
Or instead of trucks you could imagine that the left lane on highways could be replaced by some kind of train on rails that your car could dock to. In that train you’d have the same crap you have in current gas stations: mostly toilets and food stuff.
Cars docking to stuff is something that really clicks with me, but you could really go one step further away. You could split cars between the part that runs and the part that carries passengers. The part that carries people could be some kind of capsule akin to a boat container that could be loaded onto something else. When on the highway, this cabin could be put on some giant train that would carry hundreds of these capsules and when you need to get off the highway, your capsule would be loaded on some independent single-capsule vehicle, that would drive you where you need to go.
It’s probably all terrible ideas because that would make everything a lot less resilient to problems in terms of operation, but you said sci fi :-)
Oh and yeah 15 years is way too short to see that kind of changes.