My response may not offer a definitive answer to your question, but it may offer a modicum of help. Some of my project models were becoming very large too. I have employed a few ways to address the size issue in addition to purging and efficient use of layers. My approach involves judicious scene management and requires some forethought on how you will organize your model.
Develop several copies of the master model. Be aware that you don’t need to include elements that cannot be seen - for example, interior furnishings, equipment, countertops, cabinets, etc. are not essential to models when they are viewed from the outside, so I remove these elements in this situation. Place the external elements in scenes on one model. On another model place the internal scenes. Use groups to organize significant features of the models and only include those groups on the models where they are displayed in scenes. If a group is not associated with scenes in a particular submodel, then delete it.
Also turn shadows off except for specific presentation scenes that are to be rendered. Many views need not be extensively detailed with shadows, textures and colors.
I have had files that approached 100 mb, but when I discovered how to really save space using repetitive components, the typical file size has been significantly reduced, Now a large file for me is rarely larger than 50 mb and I attribute that to using low poly count components and only modeling an element that occurs more than once just one time.
I also recommend turning off layers whenever possible to conserve computing power. This requires some consideration about when you can effectively do that and about what goes on which layers. Without seeing your model, i suspect that the number of layers could be reduced.
Finally in concert with the purge command, use the “CleanUp” plugin if you don’t already have it installed.