- Go to Lightroom > Preferences.
- Also please Go to the Preferences > Performance Tab, and uncheck "Use Graphics Processor "
- Restart Lightroom and see if it works.
- Also please make sure to update Lightroom to the latest version , that is Lightroom 6.3
Let me know if it helps.
Are you doing a lot of spot healing or brushing?
Not too much but does this slow down the program?
If you do a certain amount of brushing or spot healing, it will slow down the Develop Module for that specific photo.