i personally have both specs as dual spec, my decision which one to use is based on most of the criteria described above.
biggest criteria is mana and you will go oom very fast if you dps mobs without JoW on them, but also if those fights have a lot of movement you can easily pop viper while moving and no instant shot is up. then before shotting ms and es again, just go to dragonhawk. also ms isnt a big isssue with movement fights, yes it got a short cast time, but i ll just say a skilled player can stand still for 0.5 secs, pop the shot and move on. i estimate the mana consumption with this spec to be a little more than double what you have with the 0/15/56, and thats not cos of ms, but rather due to missing TotH.
there are very little fights that require cc imo, at least boss fights, one of them is thorim in the tunnel, ms is a killer there.
an really think of any else, razorscale has a lot of adds and if you dps right you will not pull aggro on any of them.
it can be a massive dps boost on fights where you dps multiple mobs, e.g mimiron, last phase (i hope i dont spoil stuff here for ppl) but basically you dps all 3 parts with your ms every time you use it, great dps boost. also freya, great dps boost. ofc only if you can manage to keep your mana at a decent level, which quite often requires aspect weaving.
btw, you have sniper training with all specs, so even if it is a movement fight you wanna try to plan your movement that you get 6 secs of standing still at some place to get sniper training back up...