[wlesieutre]

I suspect the SE's support is tied to the 6s's, being a small offshoot model released mid-cycle that Apple doesn't care too much about.

So based on that, the 6s was the 2015 phone launch, running iOS 9. Updates in 2016, 2017, 2018, probably 2019, hopefully 2020, probably not 2021.

Last phone they dropped support for was the iPhone 5 in iOS 11. Compatibility list was the same in iOS 12 (with nice performance fixes on older hardware), but 13 is probably the end of the line for the 5s and 6.