Disclaimer: my palate was a bit muddled when I enjoyed this last weekend. However, I was immediately able to tell the difference between the 10-year expression. The oak taste in the 15 is unmistakable. The peat is more measured. The phenols were delicate, not overpowering like in the 10-year. It is a more complex scotch with a deeper, richer color and flavor than the 10.
For a second opinion, I turn to one of the Scotch All-Stars. Here is his assessment verbatim: ". . . I've remembered the official tasting notes for the Laphroaig 15. It tastes like awesome. You can quote me on the blog."
Here it is in a glass: