The Comodo installer is indeed packed with a runtime packer - the whole file (which I’d call very strange for an installer - the usual approach is to pack the (small) installer stub and then simply append the installer compressed data). So yes, the scanning of this file might take a few seconds for avast! (on a slower machine).
There’s nothing we can do about it… if you wish, you can add the installer file into the list of Standard Shield exclusions so that it’s not scanned anymore. But - how often do you really use the installer?