Welcome to the Speckle community @xTyke !
A couple of things to unpack in that question. 
If by simplify you mean to reduce the amount of geometry, you can be selective with what you choose to ‘publish’ to Speckle.
If, instead, you mean simplification of geometry for analysis, this isn’t available out-of-the-box. There is no change made within Speckle itself to the models other than to serialize the data and geometry you send to it. Your options would be to receive the Speckle data programmatically and use some whizzbang library, or more likely base a new model in another software using existing connectors – which is in essence you sound like you are doing already in IES.
So in the first instance, Speckle can very definitely help. Publish from Revit only what you need. This leads me to…
Getting data into IES; that’s another question.
I haven’t seen anyone else mention it here. It does look like an interesting platform for analysis, a bit like Hypar, a bit like NVidia’s Omniverse but for building enviro-physics. ¯\(ツ)/¯ Am I close??? And its Scottish!? 
There’s no way right now to ‘push’ or ‘pull’ Speckle data into IES.
You might like to add a request for such a connector to the Features & Ideas forum. It is always helpful to describe your existing workflow, or use-case needs when pitching for such development. I see that they have a python API, that says data and information can be extracted from models, but without delving too deeply, I’m unsure if this covers geometry creation.
Welcome again to the forum & thanks for the question! Feel free to Introduce yourself 
if you’d like.