I got a chance to sample the Glenlivet 15 again when I bought a bottle of the Glenlivet 12 last weekend; inside was a little 50ml bottle of the older expression. A few years ago I bought a gift set (for under USD$100.00!) of the Glenlivet which included the 12, the 15, and the 18. As I recall, the 15 was my favorite and when I tasted it again today I was reminded of that.
Since it was such a tiny bottle, I took it with me on public transportation and snuck in a few sips (and then it was gone). I was definitely drinking this one for fun and not for tasting, but I do remember it was very smooth and fruity. The nose was very pleasant, sweet like honey and flowers. If I ever start a collection again, the Glenlivet 15 will be on my short list.