Sounds normal. When tested with a Mity-Vac, mine started opening right around 14psi. That is the measurement you're looking for, when the actuator rod first starts to move at all. On the car, it measures 14psi under load on the boost gauge.
The pressure required to move the actuator through its full stroke (21psi, in this case) is irrelevant. Note that the actuator can move a lot farther than the wastegate valve itself can move. I think the valve's full stroke is less than 10mm? I forget...
