I've gone through the options to improve performance but still have a 5-second lag when I close a file in Photoshop CC (I used to have the same unresolved problem with Adobe Photoshop CS6). This also happens with a blank document, so file size isn't an issue.
When you close a document if there are no unsaved changes the window or tab should close instantly. If there are unsaved changes you should be prompted asking if you want to save the changes first. Small document should save and close very swiftly. Exactly what Photoshop UI are you using to close you document. Photoshop is not a file editor it saved documents into image files. Many image file types are supported some Image file types are sot supported.
I should also mention that I'm on Windows 10.
It lags even if I save a file first, it doesn't matter what format (or size) the file is - it does exactly the same thing even if it's a native PSD, a jpg.png,TIFF, etc.
Which Windows 10 I have not updated to build 1903 I still use
I have CS3, CS6, CC 2014, CC 2018 and CC 2019 installed and updated I do not have a problem like yoy describe.
You went through options to improve performance, did you reset the preferences?
I've reset my prefs and it still has the same lag.
If anyone else is having similar problems I fixed mine in seconds by going to control panel>programs>programsfeatures and then found "Intel(R) C++ Redistributables on Intel(R) 64" in the list. If you right click and chose repair it quickly fixes the problem and no more awful hanging when merely closing files in Photoshop. I'm so happy, it was driving me nuts!
Premature happiness 😞 I've tested on simple small files. Some bigger cause the same lag 😞
Is you're running FontBase font manager, try removing their plugin from the Photoshop program folder > Plugins. Removing the plugin from Photoshop (and Illustrator) solved the lag issue for me!