Actually, that sounds about right to me.
A big complaint folks make when transitioning from the real thing is their cravings aren't curbed by 12 and 18mg doses. They expect their lungs and mouth tissue to absorb the vapor molecules as fast as tar laced smokes. That ain't gonna' happen.
I tell everyone to start at 24 or even 36mg nic (if they can find it)
For cig-a-likes, ok, but not if they're starting out with a 50 watt setup like some do, nowadays.