For the ammonia, what really matters is when you see the yellow! But for recording purposes, I agree with the 1.5 ppm.
I'd leave the shrimp and do what Bpb says, once you zero out on ammonia and nitrite, do a water change. From there, I'd start ghost feeding and adding a tiny clean-up crew. I'm talking like one snail and maybe one crab. Then increase as your bioload or your tank dictates you need more.