Pinging this thread because I'm seeing a similar behavior to the OP.
While my total transfer time is reliability under a second on a recently purchased IPC-T54IR-ZE-S3 (with 2023-11-27 firmware applied), this is still slower than a 5-year old Hikvision camera that is on the same local network. I agree with
@bp2008 that
"Jpeg frames are super easy to transfer, so I am surprised they don't just have it write into memory and respond instantly with the latest image available"
With this software, the Camera Tabs are Encode-OverLay-ROI ... there is no Snapshot option there ... which appears to have been moved to a new Picture Tab ... although it sounds like that doesn't do much nor did I see a difference.
Also, the image quality from grabbing an image from snapshot.cgi is MUCH less than if you do a do a Snapshot from the Live view using the camera icon. Any ideas on how to improve the quality? I've tried adding some misc. parameters to /cgi-bin/snapshot.cgi, but doesn't seem to make any difference.