Zero config is under Value added features. It allows you to set up a template that can be used to assist in the configuration of phones for those settings that would otherwise need to be done manually. You can set up a template by the model, establish the settings you want and then apply these to the applicable phones. It is a time saver. The devices should show under the zero config tab where you then select the phone of interest and apply the desired template (if not a default for the model) and then associate the phone to an account and make other setting of BLF as needed. You then update the phone by sending a SIP Notify (the cloud icon) which then programs the phone automatically to the settings.
I suggest you read the manual about the features as it is a real time saver and may eliminate some potential errors from manual entries.
My take is that if your response time for a ping to the device is as you indicate, the network may have an issue or a lot of traffic. I normally expect to see devices that are on the same LAN segment to respond to a ping sooner than 15, but this may be influenced by the number of switches, what device conducted the ping and its relationship to the device being pinged. Given that the timeout for a SIP message is 500ms, this should not be a problem, but it may bear watching over time as I suspect the network is not being very utilized as of yet. Maybe tomorrow or when work starts up again.