Eerrr, I think that the Cessna Caravan I is only a ten seater (including the driver) so it may not be big enough. But there is a Cessna Grand Caravan 208B, which can seat a total of up to 14.
So the 208B might meet the requirement for as many as 13 pax, but not 15, and it would very much depend on which jurisdiction one is talking about since Cessna Caravan operations can be restricted to daytime VFR only and a maximum of 10 persons on board in some regulatory scenarios.