Target disk boot Macbook USB-C to iMac
I am trying to boot my Macbook through a USB-C to USB-A 3.1 cable on my iMac to take advantage of the PCI-e storage in the macbook and quad core i7 in the iMac but I can't seem to get the iMac to find my Macbook as a bootable drive, although it does show up as an external disk on the iMac's desktop when booted into os x. Has anyone successfully done this? Apple has no answers.
MacBook (Retina, 12-inch, Early 2015), OS X Yosemite (10.10.4)