My photos are approx. 4752 x 3127, version 7 in both Pse & Pre
This is a case of where bigger is not better. First, PrE and PrPro have a 4000 pixel limit on the largest dimension.
The still images need to be resized to fit your Project's Preset. This will do several things:
1.) free up resources
2.) improve quality, as PrE and PrPro do not do as good a job with resizing, as does PS/PSE.
This ARTICLE will tell you how to do Batch resizing.
Another consideration with halting Playback, is the thumbnail display. Many keep the thumbnails, All, turned on. IIRC, PrE allows one to display thumbnails in four ways: All, First only, First & Last and None (file name only). Most editors use None (file name only), to speed up Playback.
Creating and displaying the thumbnails can stress the CPU, the GPU and also the I/O (Hard Disk Drives). You might change the thumbnail display settings (little icon to the far-left of the Video Tracks, and settable for each Video Track), and see if the lag/halt disappears.