In the new Gamexplain Mario Party: Star Rush discussion with NintenDaan, he said that in Toad Scramble their were 5 worlds with 3 levels in each. This adds up to 15, contrary to the 12 we heard about. :/ Also on each level in each world their is a small, medium, and large map.
small map ~ 3 bosses
medium map - 4 bosses
large map - 5 bosses
I just thought that was interesting, very exciting!