Re: Cruise length
Actually the new regulation does not require that you do a 15 day cruise, it requires that boat operators have a 15 day schedule before they repeat any visitor sites (with the exception of the Charles Darwin station and the Interpretation center as well as airport stops).
This means that the boat has the restriction, but can divide their itinerary into several modules.
This means you could do a 15 day cruise without repeating visitor sites, but if you are short on time, it allows you to visit the Galapagos Islands on 4, 5, 6 or 8 day cruises as well.
Feel free to ask any additional questions. Have a good trip.