What plants could I put in a tank with no Co2, No ferts, and 15 watts in a 20 gallon high?
I was thinking about putting some type of easy anubias and java fern on pieces of driftwood on the gravel. Also some Java moss placed on the big centerpiece driftwood with some Taiwan moss on the floor.
Very little is going to do well under that type of lighting. It's less than 1 watt per gallon of florescent light, which isn't intense at all. The plants you're describing are very hardy but even they'll need 1-2 watts per gallon of light to survive, 3-4 watts per gallon would be best.
You also have your substrate to consider. What type of bottom are you planning for this tank?
Honestly, there are a lot of really attractive artificial plants these days, and using them in groupings might be your best option for a long term, hassle free, easy to clean and maintain fish tank. I'm all about easy to maintain these days.