Desktop refreshing icons every 15 seconds or so
Just searched for people that have this problem, because I had the same problem today. After searching the internet for about half an hour I found a little post that was old and short on Apple forum.

I guy said it is Google Drive that triggers it. I uninstalled Google Drive, and WOW my problem was gone.

So if you are a Google Drive user, try to uninstall (reinstall) and see. I say reinstall because I have had Google Drive on my Mac before without the problem, but for now, I have it totally uninstalled.

NOTE: I did uninstall with a software for the purpose, I'm using AppZapper, but there are many others of that sort. I also deleted the .DS_Store file on desktop (just in case it was corrupted). If you want to delete the .DS_Store file, you need to have hidden files shown (or use the Terminal) on your mac.