It's not like vintage port or wine, once in glass, its done and ready, and virtually stable...it will taste essentially the same today as in 1997, at least, if it changes at all it will unlikely be much improvement. 15 year old and vintage marked, that should be a nice whisky! If you have friends that appreciate Scotch, particularly single malt, it would be a great thing to invite one or two over to open it with you. Enjoy!