I wanted to add a bit more to this discussion:
I do find a fresh battery in the 6s is pretty good for battery life. Problem is the small capacity - so after using it for a few years the battery life takes a nose dive. But it can get through a working day without much issue. A fresh 6s battery should get one about 4-5 hours on screen time which is generally enough for a full day. But I noticed with my 6s, my moms old 6s, my dad's old 6s, my sister's old 6s that the battery takes a sharp hit after it loses capacity. It's still such a fast powerful phone one could make do with replacing the battery for a fresh experience
That said, the SE has the best battery life for a non plus sized iPhone, for sure. I think it's important to consider when making a decision. I had to use one recently as a travel phone and it was incredible, small light super fast can use one handed and it was fantastic when navigating especially pulling a suit case in the other direction. Has a great camera as well and fits in pockets and bags without issue. My usage of it made me fall in love with the form factor and size/weight combo again.
Hadn't given the SE a proper long term shake prior to that, but I noticed it lasted longer when compared to my 6s or 7. A quick gander online and on YouTube battery tests seems to indicate the same thing: best battery life for non plus iPhone. Pretty incredible for such a small phone!
For 50$ more you get more modern tech that will be relevant moving forward, but for 50$ less you don't really get a downgrade...It's just a different experience. Up to you what that extra 50$ is worth. I still maintain the 6s is better value overall but the SE should be given strong consideration as well.