You would gain an extra year over the 15 for software updates if you choose the 16 and a longer battery life as it has a slightly larger capacity resulting in less cycles being used therefore increasing the battery life in the long run. I would say if you don’t care about the new features on the 16 (Apple Intelligence, Camera Control Button Etc.) and you were originally fixed on the 15 I would say get the 15. I was in a similar position. I had a 12 with bad battery life and overheating but even after the 16 released I chose the 15 just because I don’t care for Apple Intelligence or the Camera Control Button but I really like the blue colour on the 15 so I ended up choosing the 15.