While I haven't been on a tour of Marriott's St. Kitts property, I have toured quite a few different Marriott properties over the years (and a number of them I have toured more than once.) Marriott tours are the only timeshare tours my wife will go on. She hates the hard sell most others use. The tours are supposed to last around 90 minutes, but if you really don't want to purchase and only want the points/$, then tell the sales person upfront. They will probably still want to take you on a tour of the facility and rooms, but they can speed it up and have you out of there in an hour or less.

Personally, anytime I am staying near a property that Marriott has a tour for, I take them up on it. I like to get a look at the facilities and the rooms and they are very low key in selling (especially when compared to most other timeshare salespeople.) So it isn't a pain telling them no. Overall, if you want some extra points it isn't a bad way to get a quick 15K points addition. ^