RESOLUTION
By default DrWeb and Qmail communicate via TCP socket. You can try to use local socket for that purpose, it should be faster.Add the following string into /etc/drweb/drweb32.ini so DrWeb would create file socket:
Socket /var/drweb/run/.dr.daemon
And the following string to /etc/drweb/drweb_qmail.conf so that qmail would communicate with DrWeb via this socket:
Address = local:/var/drweb/run/.dr.daemon
Test how it works and look into logs for the socket usage:
/usr/local/psa/var/log/maillog
/var/drweb/log/drwebd.log