why?
i think it depends on your level / game progress.
for 15day goals i build 4x each type of ovens, and finish the goal in one week.
other question is how often can you enter to do the goal.
last summer i had to spend some gems to skip / etc... coz i in the summer i'm mostly out and cannot follow as fast as now...
of course in this mean 30 days goals were perfect. you could leave for vacation, and it could not prevent you from reaching goal.
that's why i loved them. i could went somewhere to africa for couple of weeks - and no worries that no wifi: i'll get back home and do my goals.
but not now.
the goals are still doable, but now you have to choose between your real life and these virtual goals
previous order was better. at least for me. it was a game, it was meant to get fun, and you did not have to choose.
now it's more like real life - get in time or die! lol )))
and sometimes i'm starting to loose the sense of this exchange : real life "..." vs reaal life simultaion "..."