Your ClamAV scans may be slow because they are being performed as single-thread operations. Try using multi-threading to speed up your scans, which can be achieved with or without the daemon running.
To perform a multi-thread scan on the file with the path /path/to/file, try the following.
If the daemon is active, use the following command:
$ clamdscan --multiscan --fdpass "/path/to/file"
If the daemon either is or is not active, use the following command:
$ find "/path/to/file" -type f -print0 | xargs -0 -P $(nproc) clamscan