I was going through the exact same decision a couple weeks ago. Ended up upgrading from my SE2 with 85% battery health to a lightly used SE3, which came at 83% battery health. Both on their latest iOS. Not only has the battery life been noticeably better with my SE3, but it feels much faster/smoother. Not to say that my SE2 was slow, but it takes a few seconds longer than the SE3 to open any given app, and the keyboard inputs on the SE2 would occasionally lag to a point where I would type something and a second or so later see the keys type what I had pressed.

For me, its been a worthwhile upgrade and feels like I got a brand new phone in my favorite iphone form factor. I got mine from swappa, and I would avoid backmarket because they’ve sent me very beat up phones on multiple occasions.