You don’t need to remove it. Just stopping the clamd service (and disabling AV scanning in Virtualmin) is sufficient to stop paying the ClamAV memory/CPU price (which is very high…about 1GB of memory is needed for ClamAV).
But, nothing operating normally in a Virtualmin system needs 8GB or 16GB.
Something is pathological about the configuration here…though I’m having a hard time guessing what. I’ve never seen Postfix consume more than a few hundred MB (and even that is shockingly large…postfix is normally tiny).
Shutting down ClamAV and disabling AV scanning would be a good first step, just to rule it out.