I'm sorry, I am unable to check comments 24/7...
I have no idea about what could cause slowdowns on your system. The specs seems more than adequate.
I tested the game on a 2012 win 7 pc with a 2.2 Ghz i7 and it runs without issues.
I also tested on a GPDwin2 whose specs are inferior to your system and I experience no slowdowns as well with no need for /MIS1 commands
Try to see if there are too many processes active on your end that may affect the game's performance