We no longer support Joomla 1.5, 1.6 or 1.7. We will continue to make the legacy versions of our products available for download until the end of 2014, but these old versions are no longer developed or supported.
We will continue to support Joomla 2.5 until at least its official end of life - December 31st, 2014.
We will always do our best to help you if you have a problem with one of our extensions whatever your environment, but our memory of Joomla prior to 3.0 is fading and if you encounter a tricky problem, we will probably ask you to upgrade to a newer version of Joomla and the latest version of our product.
If your site is stable and working well, there is no need to upgrade it. But the more out of date a site gets, the harder it becomes to upgrade. You can put the job off for a while, but eventually something will break and you will have to upgrade. We find it is easier to keep up with Joomla upgrades as they happen.
There's a handy table of Joomla versions and support dates at http://docs.joomla.org/Joomla!_CMS_versions