May go Planted for first time.

A nice java fern paradise with a foregroun d of java tied to a flat rock is your best bet.
 
how much watts will i have with this plus the 15watt,will it work?
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I have that same amount of light over a 10 gallon Shrimp tank. I was able to grow Anubias, Java Fern, Duckweed, Guppy Grass, Anacharis, Pennywort, and Java moss. You may want to experiment with what you can and can't grow.
 
That is a 27 watt bulb I think, so you would have 42 watts in all. Pretty high lighting. You would probably need CO2 and ferts added with that setup.
You could just run the 27 watt and have a medium light tank if you want to keep it simple and low tech.
 
Wow, with 27 Watts over 10 gallons, you could grow many more plants than you can with 15 watts. Here is a good website to find plants depending on light requirements, I would say Medium High and under plants should be able to grow in your tank.
 
AquariaCentral.com