I can only assume that Haggis’s comment is a joke because that ‘that’s how the English drink whisky’.
Last time I ordered a single malt in a bar in Edinburgh, the barman asked “do you want ice?” I replied, without thinking cos sometimes my mouth gets ahead of my brain, “do you want a slap?” It all went quiet and he looked at me for a moment (whilst I thought ‘damn it, ok mate, where’s my kicking’) then he cracked off laughing, and served it in a Glencairn glass with a small jug of spring water. I felt like I’d just gone through a rite of passage.
Anyway. With a 15yo LP, I’d suggest a drop of water. I’ll not bore you with the reasoning unless you really want, but it should open up quite dramatically. A ‘splash’ is too much, you’re aiming for literally just a single drop in a dram.