There is no way to export a catalog to an earlier version of Lightroom.
You could write the metadata to XMP from Lightroom 6, and your edits (most of them, the ones the LR 5 recognizes) and some metadata will be written to the file (or sidecar xmp file) and then when you import into LR 5, these will be read by Lightroom 5. However, some things like collections and edit history and virtual copies and pick flags cannot be transferred this way.
Thanks, I feared as much. However I guess I can just export the slides as jpgs to retain my edits. I need them on the laptop to do a presentation.
Here's another question though, if rename them during the export, will they stay in the custom order I have them in my LR6 slideshow?