The old version is still available from the Force.com IDE update site. I'm not sure if Eclipse will let you easily install an older version of a plugin--you may need to uninstall 15.0.1 first.
If you'd already installed 15.0.0 and upgraded to 15.0.1, you should be able to revert to the older plugin under Manage Configuration (under the Help menu).
The old version is still available from the Force.com IDE update site. I'm not sure if Eclipse will let you easily install an older version of a plugin--you may need to uninstall 15.0.1 first.
If you'd already installed 15.0.0 and upgraded to 15.0.1, you should be able to revert to the older plugin under Manage Configuration (under the Help menu).