Hi
Firstly i strong recommend that you think about upgrading to Joomla!2.5 and not 1.5, because it's not supported either by Joomla Development Team or Us.
If you want to take this step, i recommend that you install a local server like (e.g) XAMPP and test your upgrade process.
To backup your website you can use Akeeba Component (it's free and very reliable).
Take your backup and make a local installation.
Them search on JED instructions how to export joomla 1.5 to 2.5 (there are ways and free components that makes the job)
Also search instructions on Virtuemart support forum instructions to export VM content to the newest VM version.
Only them you can install the Boutique template for J!2.5 and make your tests.
To get acquaintance and experience of the content layout of our Boutique demo, you can install a test version on your local server using the quickstart package.
Hope this ideas can in-light the your path
Cheers