Following these instructions http://tutorials.zen-cart.com/index.php?article=98
So i created a folder for my new site. And put all the 1.5 files in there.
I created a blank database on another server and imported my 1.38a database into it.
I go to install... enter all the instructions.. point it to the databse on the remote server.. enter all the details, use the same table prefix.
It installs over the top.. fresh installation.
Never asked for a database update option.
Did again, and again and again.. absolutely sure there is no update option