Other questions:
Does 1/15th mean there are 14 other owners with whom you must deconfict usage?
What is typical availability?
Do they have an on-line scheduling tool (or other records) you can look at?
How quickly have people been able to sell their shares in the past?
Do they have club meetings and would they let you attend?

The last one (attending a meeting) was the key ingredient for me deciding against my particular club option. I was fortunate to witness them airing some of their "dirty laundry" and chose not to join based on such.