The main DT Register package has moved to 2.8. As has always been the case, the package you can download is always the latest version available. And inside is the latest version for each version of Joomla.
So download, the in the 1.5 folder you'll find DT Register 2.7.19 for Joomla 1.5. The 1.5 version will never move into 2.8.