Replying to all of the above responses to my initial post, I had previously only had the Glenlivet 12, having purchased a bottle a few months ago. As a relative newcomer to the world of single malts, following many years as primarily a bourbon drinker, the G12 did not do much for me and my opinion was not changed at the tasting class. I found that I did enjoy the spicier quality of the G15 and found it more to my liking than the G18 (43%), surprising in that I find that I generally prefer single malts with a higher ABV. The class certainly had a positive influence on a few of the attendees who astonished me by purchasing afterwards a few bottles of the G18, priced at $100 at this TW&L. And I agree that at that price point, there are quite a few single malts that I would rather go for, especially in that I have discovered that I tend to prefer sherry finishes and/or some degree of peat, components that are lacking in the Glenlivet.
Finally, I have yet to try the Nadurra 16 and would appreciate the opportunity to do so, perhaps at a local rather impressively well-stocked bar nearby.