Funny they never auto-updated me on 13 and 14-- But I got 15... After that, I had to close all programs and reboot because they said I would have a RAM PROBLEM.
For my purposes, I've found it best (so far) not to have Java installed. Many users don't even need the software installed, as it does pose a security risk.
But for those who does need it, the older version should be uninstalled before installing the new. Here are the reason & instructions on the Oracle site itself:
If I do happen to need it temporarily for an app to run, such as a online virus scanner (like F-Secure), I allow the install, then after I finish whatever I'm doing, uninstall it. Being that it takes less than a minute to install or uninstall, it's no big deal for me to do so.