The template you have been using in your Joomla 1.5 web site will not be compatible with your new Joomla 3 web site. If you were using a template from a template club or another commercial template provider then there is a very good chance that they have already upgraded the template to work with Joomla 3. So you can just go to their web site and check to see if that is available.
If it is just download it and we will be able to use it in a later part of this video course. However, if you were using a free template on your Joomla 1.5 web site the chance of the same template being available for Joomla 3 are lower. So you may wish to spend a little time looking for a template that works with Joomla 3 and is close in style to your current web site. Or of course you may take the opportunity to refresh the style of your web site with a brand new template.