RE: Power metering devices (where they give you any sort of power / energy stats). Unless you use the info for something specific I would recommend configuring the devices to send the least amount of reports. For example on the ZEN15 if you only need the POWER, turn other stats off or set to longer intervals. Make sure the thresholds are set so you do not get a flurry of reports when the attached devices powers up/down. Turn on debug logging to see all the reports from the devices in the logs to verify how many reports are coming in. Try this driver for the ZEN15 (if you have 1.06 firmware) [DRIVER] Zooz Smart Plugs Advanced (ZEN04 / ZEN05 / ZEN14 / ZEN15)
Your C2 outlet seems to be the most problematic, it has a lot of hops and the most route changes. Also as mentioned it is paired with S0 which causes 3x the zwave traffic overhead.
08, 15, and 22 you said are offline? If possible I would bring them back online, your mesh could use more devices to be stronger. Are they plugs you could plug in somewhere? If so, I would try and position them so they are between your more problematic devices and the hub. Otherwise just power them up if possible. If you are not planning on using them anymore I would exclude / remove them to prevent any routing issues.
