The size of the WinSxS folder is misleading. Most of it’s contents are hard-links to other locations. Hard-links are like shortcuts, but at a lower level such that deleting the link also deletes the original and the link shows in Windows Explorer as using the size of the entire file, even though it takes even less disk space than a normal shortcut.
Thus, the folder is not really using anywhere close to 16GB.
I don’t think there is much you can do about the size.
There is this application created for Vista, don’t know if I trust it or not.