The icons that display for files in Windows are saved in an icon cache so they can be displayed quickly instead of having to manually scan and slowly load them each time.
Sometimes you may notice File Explorer loads icons slowly when you open a folder with lots of files. Increasing the size of the icon cache may help.
By default, the icon cache is 500 KB. Increasing the icon cache size to 4 MB gives the best results, but you can change the size to what works best for you.
This tutorial will show you how to change the maximum size of the icon cache to fix slow loading icons in File Explorer for all users in Windows 7, Windows 8, and Windows 10.