The technical term for this delay is 'latency'. You want a low-latency conference service. That can be expensive. I just read that big tech firms like Microsoft are offering their services free to support people dealing with the CV pandemic. Maybe you could interest them in creating 'Microsoft Singing Together' as an aid to community wellbeing ;)

What conference facility were you using? If only a few participants had a much higher lag than the majority then maybe they could fix their end, by using a cable broadband connection rather then a mobile.