15 watts just isn't enough light to grow much of anything, unless it's within a few inches of the plant. I don't know what your setup is like, but I'd be aiming for at least 30 watts per square foot. And I'd try to keep most plants, especially those you want to bloom, within one foot of the light. Good reflectors will help compensate for distance, but if your plant really has to be two feet away, you might want to consider something with more punch, like T5's, metal halide, or natural sunlight of course.

I have another light of the same 15 watt that i was going to add sometime in the future, hopefully that will help. otherwise what kind of light should i buy for an 18" hood? anything in the highest wattage, or should i be more concerned with blue/red spectrum?

could i instead use multiple compact Fluorescent Lights to save space and increase wattage? I'm looking for the most effective yet cheapest way to improve flowering

For cheap up-front costs and an 18" space, there are a couple options. Compact fluorescents like you mentioned would be a good way to go. You can go to a big box store and pick up a couple of those clamp-on dish reflectors and the biggest daylight CFL's they carry (probably 23-32 watts). Then clamp them in place, or hang them by their cords.

Alternatively, Home Depot (and possibly other places) carry this outdoor floodlight that some people (including myself) have used for both plants and aquariums.

Lights of America floodlight

It's a little more expensive, but you get a much brighter daylight bulb (65 watts at 6500K) and a fixture. The only thing you have to do is attach a cord (because it comes with two bare wires), and find a way to mount or hang it. They also carry replacement bulbs for $15.

Just buy a cheap octopus floor lamp and put in CFL's at the highest wattage the lamp can manage (usually 22W per light) and you can point them at the plants. I've used this method successfully to give more light to my orchids over winter. The CFL's give off little heat and I run them for 16 hrs. You can also use the Home Depot clamp fixtures with a large 50 Watt CFL if you have something to clamp it to. I buy the clamp fixtures with the cord already attached, about $12.00.

You are using too little light. Nothing will grow under your set up.