Is it actually realistic to sub/unsub for updates to the visible items?

To provide reactivity to the posts in the users’ feeds, first I determine which posts are on screen (I re-check when posts are added and when scrolling (throttled)).
Once I determine which ones are visible, the post starts a timer; if two seconds go by and it’s still visible, it subs to “posts.updates”, sending its ‘version’ number.

If the version number is the same (it changes with updates to the post, like edits, comments and likes), the ‘added’ fields from ‘observeChanges’ are ignored, and it’s ready to get ‘changed’ fields.

It seems to work great, but I’m wondering if it’s realistic to expect that functionality not to be too much for the server (I have between 4 and 15 posts always visible).