the complete Plan is a bit to big as file, even the opening of the File takes a few minutes on a High Power Maschine.
I have 'some' experience with this 
. I had the same problem with the big project I mentioned. I scrapped it and am completely recreating it but with every single model optimized to the max. I currently have the new project at just a tenth of the size of the original. And now it moves! (On a web page by using the Export to HTML plugin.) It also loads much, much faster.You have very nice details but they are heavy to load and display. Just removing the cars should already make a difference but there are probably other parts in your project that are very detailed, i.e. big.
In Sweet Home 3D you can add columns to the bottom left object list. Add the column 'Model size' and you can see which objects are the biggest and decide if you can rework the biggest ones to something smaller.
Careful though. Your current project looks great and you don't want to loose too many details!
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