I would try to wait until the lotus get hit by a good hard frost and go completely dormant. Then you'll need help lifting the pots. What you want to do is lift the pot and slide the entire rootball out and plop it into the new lotus bog without messing with it. (You could conceivably just put the pot and plant and all in the new pond and then fill with water around it.)
Lotus don't really need water over their crowns . . . the dirt can be almost to the top of the pond if you want it too. The 15" dirt 5" water thing will work, but you could go 18" dirt and then just keep it wet - the dirt will help hold the water and anything that lands on it will too (leaves and such).