Literally same situation here except with a 6 Plus. Upgraded this morning and the speedup and faster animations are pretty damn noticeable. Camera used to sometimes take 6-7 seconds to open which is now cut to about 1-2s. Definitely recommend the update, the new features are also pretty convenient, I especially like the new Do Not Disturb and Screentime provides some interesting stats. Now it's just battery life getting awful, but I've been putting off getting the battery replaced because spending a week+ without a smartphone is borderline impossible and I have no backup device.
Your old battery might be causing your slowness. Replace it for $30 in the store, too; you don’t have to be without it for more than an hour if they have the parts in stock. My iPhone 6a is super quick. Camera opens in under a second.
