@WeddingDJ I see! So the only way would be including all models/parts into one space, which at the moment is not a good idea, since the models are already quite complex.
Which possibilities You see for progressive loading of parts of a model. Is there a WebVR compatible streaming option, like 3d Tiles (CESIUM) or MSFT_lod so that some parts that are not used anymore could then be "unloaded" ... I guess not an easy task yet