What build is your device on? There was a security update that was pushed out at about the time you posted this thread. If you're on build LMY48M, that update didn't install...which may be a good thing. If, however, you're on build LMY48T, then the security update is installed. The good thing is that, if you're still on LMY48M, you can use the 6.0 OTA update link posted by Android Central. You may have to search for it, but it's there. If you're on LMY48T, you won't be able to use the link to update. If the security update didn't install, I wouldn't worry about it now. Just go ahead and update to Marshmallow using the OTA link.