Blender 2.8 Tutorial - How to Get Rid of Lag in the Video Sequence Editor (VSE) - How to BOOST FPS - YouTube
Viewport — Blender Manual
Quick Tip: If your scene has a low FPS and playback, you can turn on Sync to Audio to skip frames. Not smooth, but in the expected speed for you : r/ blender
108097 - The performance of Blender decreases as the number of buffered frame increases - blender - Blender Projects