The migration from Joomla 1.5 to 3.x is a major migration. These 2 versions are a world apart and with a totally different code-base. We describe here the processes to migrate you from Joomla 1.5.26Joomla 3.x (latest)
If all is set properly you can select all and hit upgrade few minutes later your site is on J3.3.6 Backup your site! (Akeebabackup)
Now your data is on Joomla 3.3.6 and you can add your new template, your extensions etc etc. It is as simple as described
We will be happy to assist you with your migration to Joomla 3.x. The fee for an upgrade or a migration depends on the size of the site. Get your quote for your upgrade or migration to the latest Joomla version!