Moved this to Quickclean and Shredder as a better spot for it.
It's not unusual to have to restart in order to delete some files, but I would be careful how you use Shredder
Tools like that are good if you know exactly what you are doing.
Regarding the slowness, that's possibly due to corruption cause by the upgrading to Windows 10.
I would do the following:
Uninstall all McAfee via Control Panel > Programs and Features
Run the MCPR cleanup tool and reboot.
Reinstall your software form your online account.
To further improve things try the tip posted in the last post here: Re: How to stop auto scanning of external drives