It’s definitely good to have detailed hands since they’ll be so close like you said, but currently VR needs to have a bit lower polycount than regular PC games. I once modeled a character for a VR game and the whole person was about 16,000 tris, so 15,000 for a hand is too high. For VR specifically, try to use as few polygons as possible and make up for the lack of detail with higher resolution textures whenever possible.
Here’s a good example of what to aim for when it comes to poly count:
Minimum detail:

Maximum detail if you really, really need it:

Source: http://wiki.polycount.com/wiki/Limb_Topology