Making large assembly into part

I have a large assembly that I want to be able to show in another assembly.  I just need it to be seen, but the details are not important.  So I saved it as a part, but the size went from 11,658kb to 92,183kb on the part.  Is there a way to get an assembly shell that I can use in another assembly, or would it just be better to put it in as an assembly an just leave it lightweight?

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