Video Sequencer terrible performance with scene strips in 2.8

Why is the video sequencer in Blender 2.8 so laggy when previewing the most basic blender scenes? I've got the default scene with the cube animating from side to side, it runs fine in the main window, but when I add a scene strip in the sequencer it runs at 1fps. And I'm talking Eevee Solid mode. If I change the preview window to Rendered mode (Eevee again) it tanks the entire operating system. It just seems completely unusable. Is this the case for everyone else? I can't find anyone else complaining about the horrendous performance. Every version of 2.8 that I've tried has had this issue.

Video files don't run very well in the sequencer either (around 10fps), but it's a whole different level of awfulness with scene strips.