Nah, 2015 won't happen, they only just started the game (though I suppose they have XV's engine to build on). Assuming KH3 will be out in 2015 means assuming it will be done by mid-year, to make room for marketting and distribution. And that would mean the whole dev cycle was what, a year and a half? A AAA game built in that little time without EA money is going to be dreck, unless the FFXV engine is worldshattering and we just can't live without another game on the same platform (full disclosure: XIII-2 took about the same amount of time built on another game's engine, so maybe I am just being facetious. And grumpy). Though I suppose we could postulate on whether or not KH3 will be dreck?
I've heard some people guess that we might get a DDD port/remake next year but I think the most likely explanation for "skipping" a year will be FFXV, yeah. It's big, it takes time and resources... it's sort of a KH game as it is, so we could just pretend it counts... Imho, we won't see KH until at least 2016, and in the west, just get comfy, unless they announced a global release and I missed it (and if they did, well then let's all get comfy). I'm personally hoping for a 3 year dev cycle. Keep in mind that Birth by Sleep took nearly 5 years, to paraphrase that great bastion of accuracy, Wikipedia (5 years minus approximately 6 months spent developing Re:CoM, apparently). Much of that would have been engine programming, but what we've got to question is 1) How much money is SE willing to spend, 2) How much time are they willing to wait, and 3) How much time the FFXV engine will save (or cost!).