PSE 15 and MacOS 10.12.3 unbearably slow

For years I used iPhoto for organization and PSE for photo editing. When support for iPhoto disappeared, I decided it was time to move everything to a new version of PSE, hence PSE15.0 and MacOS 10.12.3. PSE 15 launches okay, but once I start editing an image every command hesitates for 5-10 seconds with the spinning ball of death, then executes the command. I can't wait 5-10 seconds every time I execute a command. What is going on?