So I have a document with a lot of layers. Essentially what I would like to be able to is import a 3D shape, and use the existing layers as texture for the 3D object. Then I can edit the texture and see it applied on the 3D object in realtime.
Is this even possible in Photoshop CC?
Put your layers into a smart object.
Edit the texture of your imported 3D model (Material Properties - Diffuse -Edit texture) and copy the Smart object onto the texture as an additional layer. That way you can move the smart object around and click on it open and edit the contents.
Sounds like a very good idea. However how do I add the layers to a smart object without merging them?
Highlight all the layers you want in the layer panel by Clicking on first and Shift clicking on the last (or Ctrl clicking on individual layers) then Right click and choose "Convert to Smart Object"