Thank you for sharing the model. I think I know what is going on in this model. The technique you are using is what I describe as "direct modeling with the timeline turned on". This is a very expensive modeling practice. I won't go into too many details, but when you do a lot of Combine features where faces merge, the information needed to "track" the merged faces in later modeling features explodes and eventually becomes unmanageable. Even this earlier version of the design is too painful to work with, in my opinion. The file is 350MB on disk, and uses 17GB (that is not a typo) of memory while open.
An example of this "direct modeling with timeline" is here:

this sort of sequence where you split the body, move parts of the bodies, and Combine is the usual pattern I look for when I see these kinds of models. I suspect that a lot of the problems you have center around the brick pattern in the wall - if you are using these kinds of techniques to model that brick pattern, it would explain the issues you are having.

My recommendation would be to switch over to a fully Direct Modeling approach. Parametric modeling is useful, if you plan to go back and edit any of those features and regenerate the design. My guess, just based on what I see in this model is that you don't plan to do that. Even just the few times I tried to reposition the timeline marker in this model showed me that editing would be impractical. So, I tried disabling the timeline and exporting the design. Now, the design is only 20MB on disk, and uses only 5GB of memory when loaded. Some of that is due to the "direct modeling features" in the browser. Exporting the design to STEP and re-importing increased the size of the file to 50MB (STEP is less efficient than native Fusion for geometry storage), but when in memory, it only uses 1GB of memory. You can still use the same modeling techniques as previously, they will just not be capture in the design history.
This is still a very geometry-intensive model, and it will always be somewhat painful to deal with, but you are likely to have a much better experience if you either switch to Direct Modeling, or revisit your parametric modeling plan to avoid this style of modeling.
I've attached the direct modeling and STEP versions of this design for your reference
Jeff Strater
Engineering Director