500,000 tri-poly topology gives you loads of detail, so can easily be decimated further as you require. I have slightly cleaned up the mesh in ZBrush, where I generated a custom UV map. The 8k colour map was generated in Photoscan on the cleaned mesh, keeping the custom UVs.
• OBJ. 500k tri-poly mesh (scaled & oriented)
• 8192 x 8192 Texture map
• UV mapped