Keyword Hieararchies in Lightroom - Don't Take it Too Far!

Today I had the glorious idea to use Lightroom Classic CC’s keyword hierarchy to recreate the taxonomy for animals. Bad idea, big mistake. Now when I click on a word in the Keyword List, Lightroom freezes for seconds. I cannot move keywords within the hierarchy any more.
Now I have to figure out how to get rid of this without loosing my keywords. Maybe directly via SQLite.