While I can't speak to imaging using Imaging, I can say that doing data transfers to them from another Mac requires a third computer to act as a host, a USB-A to USB-C cable to connect the MacBook to the host, and the Push Migration tool.
You might try doing something that like that: Connect the machine with Imaging to the host via Thunderbolt, connect the Macbook via A to C cable, find the Push Migration tool, then open Imaging on your computer and see if it's recognized by Imaging.
You can use Target-disk on a MacBook (2015/6) as long as the other machine is also a MacBook 2015/6.
It is not possible to connect USB-C to FW or TB via Target-disk mode.
With the correct USB-C to USB-A (male) cable you can use the MacBook 12" in Target disk mode, and it will show similar as an external USB disk to any Mac with USB. Some USB C-A cables are for charging only, others include data.
I have one through Apple GSX, and that works for target imaging (with tools like Filewave Lightning).
The mentionded Push Migration tool is needed to migrate stuff TO the new macbook.