Given your setup and the larger containers of coco, it is more a hybrid of hydro and soilless. You could work it so that it is a drain to waste which should work well. A 15 second watering isn't much though from what I can see of the setup, as it appears that you are using small tubing for watering. I use the tubing that is made for the fish tank air lines. It is small and flexible so that I can route it haow I want, and it probably only gives about 1-2 gallons per hour flow. I let mine run for 10-15 minutes so that the medium is thoroughly saturated with water and nutrients.
I love coco because it is so good at catching and holding the nutrients for the plants. It is also very clean which makes it ideal for recirculating hydro as the water can be captured and reused many times over before needing to be replaced. I only use pots that are about 1gal throughout the grow and I get very little root growth out of the pots. I believe this is because I keep the nutrients and water, and oxygen going to the root zone so steadily that they don't go searching for anything.
If you want your plants to get really big then you can put them in bigger pots but I personally wouldn't go any bigger than 3gal pots as its not needed with soilless or hydro, and it would encourage the plants to get bigger. My plants generally get 3-5' tall and I am averaging 3-6oz dry weight per plant.
Regardless of how you water and feed, you will need to understand and follow PH of your water and/or soil. If you are using chemical nutrients for feeding your plants then you need to maintain a PH between 5.4-6.2 for healthy growth. You will get some PH drift, but if you set up a drain to waste system then you will not need to worry about the PH once it is set. The trick is to mix up your nutes and water then allow it to sit for 24hrs with a bubbler so that it can buffer itself (unless you are using AN's Jungle Juice as it has no PH buffers in it), then you can test the PH and adjust it to 5.8 which is exact for hydro or soilless. But then you still need to let it sit again for another 6hrs at least to buffer and adjust before doing a final check and adjustment of PH and adding it to your resevoir.
If you want to see how I do mine just look at the grow journal titled "stealth cabinets" in my signature. If you have any questions about it just ask. I don't mind talking about it