I too am finding that editing text using the properties palette slows down the program and causes delays/lags.
I have Rhino (6.13.19058.371, 2/27/2019) and have a Lenovo ThikPad P51 with Intel Core 97-7820HQ CPU @ 2.9 GHz, 16gb Ram, x64 Windows 10 OS.
I am wondering if the upgraded text formatting palette created some delay? Not sure but would be interested to know.