ClamAV running extremely slowly

[John F. Eldredge]

I have a laptop that can be booted into either Ubuntu Linux or Windows 10. It runs fast on Linux, but, when running Windows, it has continuous disk activity, and moves at glacial speed. My Windows antivirus software doesn't find anything, so I downloaded a Linux Live CD with ClamAV installed on it, burned the image while booted into Ubuntu, rebooted using the Live CD, and started it scanning. It has been scanning files for 38 hours now. It isn't hung, as the file names it shows as it runs are changing. Is ClamAV known for slowness?