$15 sounds a bit low. Remember the taxi's will take US dollars, but will charge in CI, so whatever figure they give you, be prepared to add 25% if you're paying in USD. Some take cards, and some do not. If they do take cards, they actually radio your CC number in, so not the most secure system ever. Bring $40 USD in cash with you, and you'll be covered for most scenarios.
The taxi fares are largely a free-for all. When I first moved to the island a few years ago, it was out of control. From my house to the airport, (about 2 miles) I was once charged $45 CI. A few of my co-workers were just sharing taxi horror stories a few nights ago, and one of them was just short of outright robbery.
In the past year, taxi complaints have been somewhat addressed. It has been brought up at numerous Department of Tourism meetings I've attended, and it is a massive complaint from most tourists on the island. DOT has a lot of power here, since 75% of the GDP on this island is tourism and they know it. Recently, (anecdotally) it seems like the fares have become more reasonable and more standardized. I'm not sure if this has been the result of any rule enforcement, or if the drivers just collectively got their act together. I think there is also a fear on the taxi driver's parts, that Uber or Lyft will be allowed here now that AirBNB has been allowed.
