Slow down DOS virtualization

I'm running Workstation 9.0, running a old PLC programming software on DOS 6.22. Can run program on pc that I can lower the clock speed on (~80MHz). When you try to start the program you get a "Fatal error 70FE". I can lower the base frequency on the motherboard until the software just starts working. Is there a way to some how slow down the virtualization to mimic an older, slower pc? Thanks