Ethernet switches might be capable of 15,000 to a million packets per second. I do not think 24 packets (12 requests, 12answers) will stress it very much. But this is not a networking performance advice forum.
Whether you have to do this polling, or you can instead set up your cameras to send unsolicited messages in response to real events is a function of your cameras capabilities. There are only the two ways to do this.
wow great to hear 
now i can buy more cameras
lets just hope that node red is up to the task
thanks for all the help!
After some tests, i can say, that one second it is really not enought, it looses many movements.
But i thing the probem is not in switches, but in resources of platform that computes this requests.
Buy better a normal camera that sends movement by itself without polling (read - with support of motion detection by OH)
Realy to say, Reolink does it, but it do not supportted by OH, so you need to poll it.
do you know of such ? 
i was sure the reolink is the one , but i am planing to buy 10 more so if you have any wisdom please share
maybe @matt1 can tell us what is the most feature rich for this kind of use
There is a topic in Community.
Search for something like ip camera binding. The biggest one. The is a list of compatible cams like dahua and so on.
Nativly reolink support it in onvif, but this binding do not work with it. I tested it for half year, maybe now smth changed. Read that thread.
I believe something has changed as we have a few users of reolink now using the binding.
@Gad_Ofir
The cameras with the most features are the ones that are both api and Onvif. This post Linked below breaks it down. I would not go for a non onvif camera as you gain a lot by having this as a bare minimum.