Macallan 15yr Fine Oak, like all official bottlings of Macallan, is overpriced...it's also hard to find in stock unless you walk into a random cheap liquor store and find a dusty bottle.
Furthermore while the distillate is from Macallan, a Kirkland branded bottle is likely aged in different wood under different warehousing conditions. Whether the whisky is matured in first-fill bourbon or second/third-fill matters. Maybe it was aged in a hogshead fashioned out of old staves by a cooperage in Scotland. Was the sherry butt used for finishing the whisky Oloroso, Fino, Amontillado, etc? Macallan doesn't 'finish' any of its official bottlings AFAIK, so that also changes the flavor a bit.
I will say however the Kirkland and Trader Joe's bottles are very drinkable, especially for non whisky drinkers. It's a good bottle to have for gatherings as anyone can enjoy it.