It's a bit of an assumption to say that you're not a whisky drinker based on just those two bottles. While I've not tried the 15 year old, to me Glenfiddich 12 year old is rather uninteresting. I recall something fruity and honey sweetness but nothing else springs to mind—not something I'd spend my own money on.
With all the different distilleries and individual expressions, there's a wide range of whisky to choose from. If Glenfiddich didn't do it for you, try something smokier from the islands, like Talisker 10; maybe a peaty Islay like laphroaig 10 or Ardbeg 10; or maybe something more sherried—I hear good things about Macallan's range, Glenfarclas 105 is excellent, too, or an Auchentoshan Three Wood if you like a bit more of the vanilla-like flavours.