i just tested it and your onto something. the bug first showed up on a table that definitely has fifteen plus rows. i just tried to recreate the bug on table with less than ten rows and i didn't notice any lag.
power mode is off
Viewing post in Table Bug
I have some (small) performance improvements coming in the next update that should improve this. It’s nothing huge, but may help on your system.
As a workaround, you can disable automatic table formatting (Settings > Input > Table formatting), and use key shortcuts to manually format tables instead: https://support.deepdwn.com/docs/guide/shortcuts/#tables