I started at 15mg, dropped to 12mg and now hover between 10-12mg steadily. I didn't get into vaping to completely drop Nicotine, rather, drop the harmful aspect of smoking dried plant material. I enjoy the throat hit that the Nicotine provides, something that has not yet been easily replicated.
I was a pack / day or less smoker, so I didn't stay at 15mg too long, about a month or so. At 10-12mg, I get exactly what I need without any issues and it's consistent enough for me. I'm smoke-free now and enjoy vaping for what it is and what it's done for me (i.e. no more horrible breath, no more continuous back pains, no yellow teeth, no smelly clothes etc).
That being said, I don't have any plans to drop to zero-nic until we have a way to fully replicate the throat hit that nicotine provides. The substitutes that are available simply don't measure up for me, IMO.