can I somehow avoid redefining my instance geometries in I3DM for each tile although I use the same 3D model in each tile?
Currently I embed instance geometries as binary gltf. Would referencing to an external URL from a library help?
Yes, referencing external gltf’s should do it: https://github.com/AnalyticalGraphicsInc/3d-tiles/tree/master/TileFormats/Instanced3DModel#gltf