Hi Paul,
I'm somewhat shocked that you would even still consider using a Joomla 1.5 website. There is no support for it anywhere and it is very unsafe to use as there have not been any security updates for years. It is really a disaster waiting to happen. I know this is not an answer to your question, but I would strongly urge you to upgrade from 1.5 to 3.5 if you don't want to get into any trouble sooner or later.
Cheers,
Thom