External Camera Photo Sphere File Size / Resolution

[Big Spherz]

I'm definitely a newbie at photo spheres. I've had no problems creating one with my HTC One M8. However, I'd like to move on to creating them externally with my Nikon D800. As this is a 36 Mpix camera, it seems like overkill to create giga pixel file for displaying one a 1k HD phone screen. I've searched the web but, haven't seen advice on this matter. Some practical advice please.