So you still use Joomla 1.5 ; well you should know this version was EOL for more as 3 years, but that does not help much.
You should upgrade to the latest supported Joomla versions as soon as possible. 

You can't yet ? check out this article for some great hints and tips to use Joomla 1.5 with minimal risk (for as far that is possible) keep in mind that the article only talkes about the Joomla core; you may have components or modules which are not updated anymore as well and can have security issues too.

Link: https://vel.joomla.org/articles/1877-morals-or-money