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I had this infuriating problem too, but was able to overcome it entirely via following technique.
(Note: I'm using INDD 15.1.2 on Windows 10 in late August 2020).
Adobe should note that this is a workaround only and not a total solution to their bug.
In this thread there is a post by: Anonymous on May 29, 2020 13:49. which states:
"removing the Document Fonts folder (for a packaged indesign document) so no fonts were loading from the packaged Document Fonts folder. If even 1 font is still in the folder I get the problem, which also includes extreme lag when switching into or out of the text tool and selecting text."
Further to this, I then closed and re-opened document.
Hope this helps some people.