Firstly, with regards to the above answer, lights can be on for as long or as little as you like. If you have live plants, aim for 10-12 hours a day.
The type of lamp will have no effect on the fish whatsoever...they don't give a damn. It's the plants that will appreciate "proper" aquarium lighting. The wattage of the lighting will depend on the length of the tube so 15w is not an appropriate guideline
I have a 600 L planted tropical tank and i use 10 x 18 watt energy saving lights and the tank looks awesome.
Most fish will feel more confident with lots of hiding places. If you add clumps of plants, rocks and caves etc, the fish will tend to come out more.
Give the existing fish time....they will grow more and more confident. Keep the lights on and leave the tank alone. Don't add any more fish for a week or two, maybe feed two or three times a day but with just small amounts of flake.
Do you have a filter or any oxygen going into the tank ?