Spot Removal tool, local corrections, and History panel

The Spot Removal Tool and Local Corrections Brush are not designed for hundreds to thousands of corrections. If your image contains many (hundreds) of localized adjustments, consider using a pixel-based editing application such as Photoshop for that level of correction.

If you have many corrections, check your History panel. The History panel has no limits, and it isn't deleted unless specified. If you've been creating many local or spot corrections, your history could be long, which can slow Lightroom's performance as a whole.

Clear the History panel by clicking the X on the right of the History panel header.

Order of Develop operations

The best order of Develop operations to increase performance is as follows:

1. Spot healing.
2. Geometry corrections, such as Lens Correction profiles and Manual corrections, including keystone corrections using the Vertical slider.
3. Global non-detail corrections, such as Exposure and White Balance. These corrections can also be done first if desired.
4. Local corrections, such as Gradient Filter and Adjustment Brush strokes.
5. Detail corrections, such as Noise Reduction and Sharpening.
Note: Performing spot healing first improves the accuracy of the spot healing, and ensures the boundaries of the healed areas match the spot location.

Quoted:
My C drive only has 20gig of 250gig free.  SSD.  I have Lightroom installed on that drive, but my catalog is on an external HDD using USB 3.0.

I'm going to free up space and see if that helps any.

Edit:  Freed up 65gigs, enabled smart previews while editing.  Works great now!