I'm guessing you're an experienced windows user so guess you had the system running at a good speed previously for comparison. Normally Malware and AV software will do a full system baseline scan in the background. Cold this be the impact? has it been a while since the reinstall?
As a side I gave up on full blown AV / AM software because of performance impacting tasks. Now I just use Defender native and through this control and personal controls haven't yet had an issue. Yet. But if the laptop is to be used for risky stuff, torrenting etc that might not be a good idea.
Finally assuming you formatted you HD and didn't do a reinstall to a new directory.
