You can not grow with any light.. A UV light will certainly not give your plants the light they need.. 15W is under powered for sure.. A nice all around number is about 100 watts a plant.. But that's only a base or outline.. generally speaking I run about 200-250 watts of led per plant. I'm not gonna tell you what diode to use or what drivers.. Because they are numerous ones that perform in the 2.0-2.9 range.. There is a ton of more information that I could pass along. But I will tell you I have tested all sorts of lights with my fancy high value meter and you absolutely don't have to spend thousands.. But you do have to spend some money to get "worth while" performance.