Previews are erratic, and fitful, even after Rendering

Nobody has been able to explain why my video previews don't run smoothly, even after rendering with the "High Quality" option.

Everyone I've talked with about his says they don't have this problem and don't understand why I do, considering my equipment.

I am currently using PrE to make short slideshows.  My project settings are set to default.  My images are 2500 px on the long side, with a resolution of 300ppi.  Each slideshow contains 7-10 images with lots of keyframed pan and zoom.  There are usually a couple lines of text, keyframed to animate, a soundtrack and a narration track. All the images have crossfade transitions.

Would changing ScratchDisk options have any effect on this problem?

While previews are a major frustration the export files run smoothly

Windows 10 Pro

v 1607

OS Build 14393.1715

Intel Core i7-6600U CPU @2.60GHz 2.81

16 GB RAM

64-bit OS, x64-based processor

Intel HD graphics 520

NVIDIA GeForce GPU

475 BG SSD 191 free