For a medium complex part (69 features, 3 solid bodies) - 3.36 MB in SW 2015 versus 4.04 MB in SW 2014!!!

For a fairly large assembly file set (4754 components, 1360 unique files, including Toolbox files) - 417 MB in SW 2015 versus 804 MB in SW 2014!!!

Please test on your systems and let me know if you find the same thing.