Glenlivet 18yo vs Glenlivet 15yo Reserve?

So I finally decided to get myself a bottle of fine scotch and since somebody recommended Glenlivet and it's readily available I decided upon that (it gets fairly good reviews too from the looks of it). Anyway, I was wondering which is the better choice, the 18yo or the 15yo Reserve. The 18yo is obviously aged 3 years longer and is slightly stronger (43%) but the 15yo is aged in the high quality french oak casks. Normally I would say go for the 18yo but where I am there isn't a lot of variety so the only 1L Glenlivet bottles are the 15yo Reserve bottles. Since the difference in price is not that much, I figured if they are almost equal I would go for the 1L just to have a little more of it. If the 18yo is better by far I will definitely buy that though. Could anybody help? Thanks in advance.