How do you adjust Joomla defines?
From Joomla! Documentation
The "J1.5" namespace is an archived namespace. This page contains information for a Joomla! version which is no longer supported. It exists only as a historical reference, it will not be improved and its content may be incomplete and/or contain broken links.
Edit your /includes/defines.php file. Below is the relevant code.
define( 'JPATH_ROOT' , implode( DS, $parts ) ); define( 'JPATH_SITE' , JPATH_ROOT ); define( 'JPATH_CONFIGURATION', JPATH_ROOT ); define( 'JPATH_ADMINISTRATOR', JPATH_ROOT . DS . 'administrator' ); define( 'JPATH_LIBRARIES' , JPATH_ROOT . DS . 'libraries' ); define( 'JPATH_INSTALLATION' , JPATH_ROOT . DS . 'installation' );