Wh is a measurement of energy, but W is a measurement of power (that is, the rate of energy). They are different units of measurement and you're mixing them up here. Here, you've doubled the original rating of 15 watts up to 30 watts; that's the result of the confusion between energy and power. You don't divide the wattage in half when you run it for half the time, nor double it when you run it for twice the time; that's not how power works. That's how energy works.

In your original post, the number was 15 watts, and you figured it produced 5 ounces of water in 30 minutes. So you then figured that 3 watts can produce 1 ounce of water in 30 minutes. So far so good; that's correct. If the panel continuously produces 3 watts of power (remember: watts are a rate of energy) over a period of one hour, that's 3 watt-hours of energy. For 30 minutes, it's 1.5 watt-hours of energy. Thus, it took 1.5 watt-hours of energy to produce 1 ounce of water. (1000 watt-hours) * (1 ounce / 1.5 watt-hours) = 666 ounces.

It may make more sense to translate this into distance, which I think is more intuitive for most people. Watts (power) are like miles-per-hour (velocity), and watt-hours (energy) are like miles (position). The panel runs at 15 MPH. After 30 minutes it has run 7.5 miles and produced 5 ounces of water. Thus, it could produce 1 ounce of water by running just 1.5 miles. It still runs at a speed of 15 MPH no matter what.