Other than specific raid break points, are there any noteable instances where a 14a/15d/15s Dnite would perform worse than a 15a/13d/13s?
It can hit an undesirable defensive breakpoint, but that's highly unlikely to matter with a two-bar charge move and Dragonite's overall tankiness.
Other than that, it's all about the offensive breakpoints. It's possible that in some matchups DT has a breakpoint at L40 for 15 attack only, which would actually matter. In a fair number of matchups it probably just misses an Outrage breakpoint and deals 1 damage less with that, which has a minuscule effect.
I would power both anyway. I have a 14/15/15 and 15/13/13 and I probably prefer the 14/15/15 more (if you fight a raid boss that you don't resist, such as Raikou, you will see a somewhat noticeable damage taken increase with the 15/13/13). Fighting something that you resist (e.g. suicune/entei, solar beam ho-oh), the defensive IV usually doesn't matter.
If you do decide to power both I'll give 14/15/15 hurricane and 15/13/13 outrage, as you want the more survivable one for multiple hurricanes.
Walk the Dragon :)
If that's your situation then I'll power the 98 for the following reason: Your main 'candy source' would actually be hatching 10k eggs, and sooner or later you're bound to hatch a really good one while you wait for candy to power your 98.
Remember, there are many better dragons than a 15/13/13, but only 15/15/15, 15/14/15 and 15/15/14 beat your 98%.
