Have read if they are low that oil will get in the wrong place? Does it go back when pressurized to the correct setting?
So 150 is the correct number to shoot for?
If the N2 pressure is zero, the oil will get into the pressure chamber. This causes low oil level in the shock and an air pocket. Repressurizing them will not put the oil back into the proper chamber. If your lucky and haven't really worked the shocks hard you should be OK. One way to test if oil is in the resi is to let the N2 out of the valve and see if any oil comes out. And as noted always fill shocks extended.
150 is a good number for what you are using them for.