Is it enough Water?

You can water your soil untill it is just about to see run off. You do not want any. I am also in 15gal container and a good watering is about 2gal. A deep watering help to assure that all the soil is moist. My ACE plants are a little bigger though... I water twice a week. Second watering is done 4 days later with about half quantity. Water uptake depends on RH, Temp, plant size, air circulation and stage of growth: not saying you should do a copy paste but it can help. Key is to no water again until soil is getting dry 3-4 inches on top and container is getting light, still before plant start to drop. Hope it helps!