The input is isolated from the output, to avoid possible ground loops - this is in an audio device.
The PSU is on a separate PCB with a 3 pin connection leaving it (for +15, GND, and -15). There is also a 2 pin connector for a power LED, powered off the -15V.
I currently have a common mode choke on the input, since I noticed it made things a lot less noisy during my breadboard testing with an oscilloscope.
Basically I'm just wondering what best practices are for ground planes, if there should or shouldn't be any - especially under the CMC, inductors and DC-to-DC itself. And what that ground plane should be connected to (unconnected, input voltage ground (before or after CMC), output voltage ground, etc.). I hope that helps.