The model is 1.5gb.
How large is it in number of polygons?
In VR, especially with say a Vive headset, you need really beefy graphics performance as the headsets run at 90-120 frames per second and less will cause stutter in the VR experience. Displaying in stereo (left/right eye) potentially halves the framerate, but modern VR viewers can use tricks to make the performance hit much smaller than a factor of 2.
In practice, the model might need to be simplified quite a bit to be smoothly viewable in VR.
I need to know the best format to export out. And which software to view the model in.
These two are related, as the viewer you're going to use will dictate what kind of format to export in (or need to convert to). Good general 3D model formats are Autodesk FBX (binary, lots of features), Collada (XML-based), Wavefront OBJ (verbose as it is text-based) or PLY (binary, but does not handle textured materials).
Sketchfab.com has a VR-viewer, but it requires you to upload the model to their site, which might not be what you want. You can use Unity3D, but that requires you to do some scene building (and even some programming). The Vive comes with an application called Workshop that allows to add and view 3D models, but it's a bit convoluted (
https://developer.valvesoftware.com/wiki/SteamVR/Environments/Photogrammetry)
I actually don't know any good standalone VR viewers for 3D models.