I don’t think you have enough run that big of membrane, but I suspect your close. I think you need as a min .8 GPM
However if you fed it 1.6 GPM, it would make 20 gallons per hour. That is the max that membrane is capable and 1.6 GPM is excessive, but apparently an excess isn’t harmful.
However you may get close to 20 GPH, but I don’t know if not having enough flow will shorten the membranes life.
Look at Cruise
RO watermakers to get an idea
His 20 GPH is a single
membrane with a 1.6 GPM pump, the 30 adds a second membrane, the 40 adds I believe a 2 GPM pump.
So of course it’s a function of both how much membrane surface area you have and Water flow, I believe as a rough example you need three times the raw water
flow than what your product water flow will be. Too low a flow rate will I think reduce membrane life, too much isn’t harmful but wastes power.