Had a curious situation where items based on a certain template took forever to load in sitecore tree. Turned out the template had some fields where for some items A LOT of data (jurusdictions) were loading.

Fix: click the Sitecore button (where you get licensing info) and uncheck Prefetch Collapsed Sections. Then find an item based on that template, collapse all sections and uncheck Standard Fields.

From there every new item I open I can see the item much faster.