Contribution Page Time to Submit
17 seconds from pressing &quot;Submit&quot; to the thank-you page is still obscenely high.  My only client who comes close to this has maybe 80 extensions installed.  My guess is you have something going on already that's exacerbated by Stripe.
While it's not the easiest solution, doing an xdebug profiling session would be really helpful here.  E.g. I once found a bug in the token processor that made contact creation take a long time - and when I added an extension with custom tokens, the problem got even worse.  Something comparable may be happening here.