I took a look at your Blender file, and I do not understand your texturing technique. You seem to be applying a number of overlapping texture maps to the same geometry. simplepbr supports a single base color/texture per node, but you can arbitrarily divide your model up into a bunch of nodes to apply as many textures as you please to those specific parts of the geometry.
Realistic Office with PBR Lighting In this example, my Blender file is about 140 megabytes. Panda has no problem with that.