Joomlablogger.com posted an interesting article on why you should be upgraded your Joomla 1.5 page.
There are many direct and other long-term reasons. The safety and PHP / MySQL support is something that worries then Joomla 1.5 will soon stop receiving updates.
Read article here
To begin with, the whole core engine / platform brand new and now has version number 11.3. News of the platform is that it is now easier for developers to make features such as editing image files, and it is easier to generate the table code. The new platform also has the new MooTools 1.4 integrated.
More news is a new smart search feature that dynamically helps users with suggestions for search terms during the time they are printed. This we have seen for quite some time on Google and it's nice that it now also become a natural part of Joomla.
Spam and fake accounts are now history when Joomlakärnan supports reCaptcha immediately upon installation. Before, you had to rely on third-party functions for this.
In virtually all of the administration has been simplified with multiple selection for operations such as copy and move.
Yes, this is just a small scraping the surface of what's new. Read this article for more info ...
Many new items are promised and we are really eager to start testing. Joomla 2.5 is a so-called LTS version (Long-Time-Support), which means it will fixes and updates in 2 years, which makes it a very safe and good bet for your new website.
If you have an older version of Joomla and want to upgrade? Read more here...