Render results so far:

Straight out of the box the scene rendered on my machine in 15 min, so quite comparable to your results, which I was greatly surprised by.

Then I started shifting it closer to what I am aiming for: One of the first changes is adding the render passes. I need them in my workflow for post, so I never render without them. I added all the usual passes I render and re-rendered your scene with nothing else changed: 20 min. Still quite good.

Now I replaced your model with the classroom I was using before and immediately the render time shot up to over an hour (attached file - 1 hour 12 min render). And that is without the replicated lights or any other requisite items - just the bare classroom. So I am guessing the issue is in the model and, possibly, my shaders. The shaders had little influence on render times as I was changing them, but I intend to experiment more with them. I will post my results as I get them.