Two requests every 30 seconds is barely anything, so I’d say it’s nothing you should be concerned about. If we’re talking two requests multiplied by thousands of users then that’s something else however…
As far as I know there is no limit when you provide a client id, and any app that gets unusually high will get reviewed on a case by case basis, and then contacted by the devs directly.
As with any API, if you’re serving multiple users the same data, or there’s a lot of data reuse, having some caching mechanism is good practice. This doesn’t seem to be relevant in your case though.