About 2ounces per second.
How about we restrict bathtubs to no more than 10 gallons with mandatory overflow valves?
Anyone with any brains whatsoever know how to hack a shower head to get the flow they want.
Actually, 1.5 gallons is 192 ounces divided by 60 seconds is 3.2 ounces. You were off by an ounce which makes it a real soaker, eh?