Photoshop very slow to close files
I had the same problem after updating my nVidia graphics driver. In the nVidia settings panel I changed the 3D settings for Photoshop.exe to "Powerful nVidia Processor" instead of the "normal" setting. The problem was solved after that.
I experienced this same issue in Photoshop CC 2018, Windows 10 Pro on a PC with integrated graphics (Intel Core i7 3770 - Intel HD Graphics 4000). I found that if I unchecked the 'Use Graphics Processor' option in Preferences/Performance the issue stopped.