The page for the Media Creation tool now says that it can not be used to upgrade to 1511. I guess, (actually I know for a fact) that others, besides me, could not get it to work. I guess I'll throw away my burned disk of 1511 too since that probably has the same bugs that prevented the tool from working. They said they have not pulled the update from WU though but I bet that when the ones who haven't received it yet finally do, they will get a patched up version. I still have not seen it btw.
Come to think of it, I do remember checking the version number of setup.exe in the tool created ESD folder and seeing that it said 10240. That was the first time I tried it a week ago. So, now, it looks like they have pulled the 1511 ISO from the tool completely since some people weren't getting it anyway.
With all the reported problems with the update, I'm now kind of glad I haven't gotten it yet.