As Shizeric writes, the lighting is no problem as long as you provide ample hiding opportunities for the Axies, indeed they would prefer no light at all but that makes the tank rather boring to view, and rules out having any live plants in there.
The main issue i find with lighting for Axolotl tanks is the heat produced by it, now i dont know what kind of a tank you have there, but if its of the kind with a hood with built-in lighting (i guess since those are commonly sold with 15w lights), you might find it very difficult to maintain a cool enough temperature for your Axy.
Personally i keep my tanks with a mesh covering, and the lighting is positioned 1 feet above the water level or so, makes it much easier to maintain the right temperature.
Good luck with your new pet!
Regards Bjorn
