I've been helping quite a few people set up Jitsi lately. The software works reasonably well, although documentation is lacking and a lot of configuration options are named terribly, but one thing I've noticed is people's expectations about bandwidth usage are way lower than actuality, especially outbound from the server. But a bit of napkin math suggests that Jitsi isn't doing anything fundamentally inefficient here; one high-res stream plus N low-res streams transmitted to N participants is just a lot of bandwidth.