Hi. This lag may be because your GPU specs are low for Photoshop's recommendations, but any number of things may be affecting it - file size, filters, etc. It takes time for a file and it's instructions to be written and verified by an OS. You can see a progress bar at the lower left of your window, indicating the stage of open/save you're in, as it happens. One thing that may be happening is also PS checking the online cloud info, and font info that you may be syncing with. Please try using your computer on a wired connection for greater speed than Wifi generally gives.