Php Fatal Error in 2.5.15
From Joomla! Documentation
The "J2.5" namespace is a namespace scheduled to be archived. 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 It exists only as a historical reference, it will not be improved and its content may be incomplete and/or contain broken links.
A fatal error has been found in Joomla 2.5.15, when used with PHP 5.2.
What is the cause
A non-PHP 5.2 compatible function was used in the JHttp class.
How to fix
Please update to 2.5.16