iMac 21.5 late 2009 and Zoom Conferencing - Lag

[photogramps]

Enjoying my first venture into Mac with my 2 x iMac 21.5" late 2009 - I've upgraded both to SSD's and it's been a great improvement.
Over lockdown I have been using Zoom to join with others in groups of 3 to groups of 100+ and the only problem that I am experiencing is varying delay/lag between video and audio (video lagging behind).
I am wondering if my iMac just isn't really up to the job or if it's something else that is more likely causing the problem
One iMac is on WiFi and the other on Ethernet - I have a 40mb Broadband connection and its normally not far off that on Speedtest.
There could be up to five pieces of equipment connected to the Broadband but only two would be 'actively' using it.
Any observations/suggestions most welcome

 

[FNH15]

Enjoying my first venture into Mac with my 2 x iMac 21.5" late 2009 - I've upgraded both to SSD's and it's been a great improvement.
Over lockdown I have been using Zoom to join with others in groups of 3 to groups of 100+ and the only problem that I am experiencing is varying delay/lag between video and audio (video lagging behind).
I am wondering if my iMac just isn't really up to the job or if it's something else that is more likely causing the problem
One iMac is on WiFi and the other on Ethernet - I have a 40mb Broadband connection and its normally not far off that on Speedtest.
There could be up to five pieces of equipment connected to the Broadband but only two would be 'actively' using it.
Any observations/suggestions most welcome

My 2018 15” Pro lags in Zoom, but only when I’m screen sharing (my fans also spin up - sounds like a jet!).
What OS are you running, and which processor’s in your 2009?

What does Activity Monitor show when it’s lagging?

 

[photogramps]

My 2018 15” Pro lags in Zoom, but only when I’m screen sharing (my fans also spin up - sounds like a jet!).
What OS are you running, and which processor’s in your 2009?

What does Activity Monitor show when it’s lagging?

Thanks for the response.

The OS is High Sierra and the processor is 3.06 GHz Intel Core 2 Duo.
I don't know about activity monitor, I'll need to check that next time I am on Zoom.