There will always be a slight delay in a live feed due to the need for it to capture then send to the screen you are viewing from.
I use a hikvision and hilook onvif camera at the moment that are going through a 5 port tp-link POE switch then into my main 24 port hpe switch in my rack and one hilook that is going via a POE injector then into mesh node that conects via 5Ghz backbone to the main router that feeds into my synology nas I am using as my NVR. (internet side access is blocked for the camera’s specifically)
I have HA use a shelly button 1 via an automation to capture an image the moment it is pressed as a doorbell action and send it to my phone via notification for the front door camera whilst the main feeds I view view DS Cam (I use openvpn via my router on the phone to connect to it for near live feeds when I am out especially when I am on a 5G connection at the time.)
I run my HA instance on a Intel NUC5i7RYH in a passive cooled case in a virtualbox instance currently with little to no issues other than my BT dongles being dead for passthrough.
edit: added more info for reference for those looking to setup similar to mine if they are having issues with pi’s etc