[kps]

The non-S iPhone 6 was discontinued at the same time, and did not even get iOS 13 one year later.

[Jtsummers]

The 6S has 2GB of RAM versus the 1GB of the 6, probably the principle differentiator here as otherwise the specs look pretty comparable (6S also has 2 more GPU cores and a faster CPU clock rate which may be other contributing factors).

[tompazourek]

That's sad, but it's at least getting security updates for iOS 12, and quite frequently.