I tried to import the RTF file of 1.61 MB into the newest Beta of Scrivener for Windows. This time I could not even import the file. This made me think that perhaps the issue has to do with the fact that Scrivener for Windows has issues with certain zip formats. Atlantis saves "supercompact" RTF files (i.e. compressed files).
I opened the file in Open Office and saved it as a DOC file. This file imported into Scrivener without any problems and the speed issue is gone.
It now works as promised. Sorry to have been so quick to judge. I'll give it another trial.