<15ATK for legendaries

I think for any particular IV stat and mon, you could find some breakpoint to justify wanting the 15 attack, which doesn't change the fact that the difference between 14 and 15 is a very small percentage of total attack stat, and in most cases, it matters not at all.

Bulk points are harder to calculate, but the additional defense or stamina could make the difference between getting a charge move off, or not. If so, that would outweigh any breakpoint advantage. Anyway, for most mon, especially legendary monsters, I always go for the highest total IV. The exceptions are mon like blissey where the attack stat is pathetic in comparison to the other stats, and 1 point of IV is more likely to make a consistent difference.