Turns out that our recent update for the free TextExporter plug-in for InDesign was running much, much slower than it should on any reasonably sized document. Version 2.0.9 fixes this abnormal slowdown. Go to get it here:
https://www.rorohiko.com/textexporter
TextExporter is a free plug-in for InDesign that export all the stories of an InDesign document into a single file (RTF, InDesign Tagged Text or plain text).