Simplygon is a polygon  reduction tool, one that I have used with great success in a few projects. It can be used to simply reduce the triangles in an object like we would use in this particular project, or it can be used to create level of detail (LOD) models. These are series of single models that contain fewer and fewer triangles as you get further away. These are more ideal for big game projects than what may be done in a HoloLens project. Simplygon was recently acquired by Microsoft, so hopefully, it will be integrated into the workflow eventually.