Fix #1: Optimize
If Lightroom has been running great then suddenly you notice it has been slowing down, your first task should be to optimize your catalog.
- From the File menu select Optimize.
- A dialog box appears informing you when the last time your catalog was updated. If it has been a while, click Optimize.
Fix #2 Preference Settings
Usually optimizing your catalog does the trick but if you really want to gain speed a few adjustments to your preference settings will really speed things up.
- From the Edit menu select Preferences.
2. Lightroom CC/Lightroom 6 can use a compatible graphics processor to speed up adjusting your images in the Develop module. Select the Performance tab and place a checkmark in the box next to Use Graphics Processor.
3. Sometimes a cache file could be bloated with a bunch of temporary image information you no longer care about plus take up extra space on your hard drive. Starting fresh and forcing Lightroom to rebuild it with only the images in your catalog can save you disk space. Select the File Handling tab and click Purge Cache found in the Camera Raw Cache settings section.
By default, Lightroom sets the Camera Raw cache to 1 GB. If you increase the cache size, it can store more image data, which in turn speeds the generation of previews of those images. Increasing the Camera Raw cache to 10 GB or more can dramatically speed performance in the Develop module. To increase the Camera Raw cache size, select the File Handling tab and change Maximum Size to 10.
Restart Lightroom to apply these changes
Now that you optimized your preference settings, the next time Lightroom feels a little sluggish, you only need to optimize the catalog.