From the beginning, I always found MSE very slow and heavy on resources.
I just barely had my 1st and only ... and very brief experience with MSE recently when I was having computer problems that seemingly pointed to avast. I tried MSE for only around 3 days. Wooooooo! Yes, it is noticeably slow in the regular course of things. But, in a manual FULL Scan, it was super, mega, ultra, ridiculously Ssssss SLOW!!! At the end of 30 minutes, as per where the progress bar was, I calculated that it looked like it was going to take 8 hours to complete at the rate it was going.
So, I aborted the Full Scan and uninstalled MSE right then and there.
Yadi Yadi Yada ... after then not being able to even get Avira to install properly ... I finally threw my hands up and desperately performed a Windows Reinstall System Recovery. My computer then worked properly again. Man oh man am I glad to be back to avast!