After doing a search for Joomla! 1.5 templates, a Site Ground link was one of the top results. For those not familiar, Site Ground is a web host that specializes in Joomla! hosting. They also apparently offer several free Joomla! 1.5 templates as well.

Here's a nice collection of four Joomla 1.5 templates. To download the templates you must register for free with Site Ground.

Equalizer View Demo Download	Palette View Demo Download
Site Ground View Demo Download	Fall View Demo Download