Hi,
j1.5 is extremely dangerous to use on a live website. Even a teenager hacker can easily hack your website. You must seriously consider upgrading to Joomla2.5.
This is actually the reason why we have eliminated all the j1.5 from our servers. Because we don't want to be hacked.
Last year we have stopped supporting and providing updates for j1.5 and VM1.1.9 extensions. (just like what Joomla and Virtuemart official developers do. They all stop providing support and updates for old versions)
Our Module was supposed to work on Joomla1.5 and VM1.1.9, but the one that works is the old version. The new version is only developed for VM2.x and Joomla2.5.
Regards,
Support