I would like to know the meaning of "in" in the next sentence.
Shape up in as little as 15 minutes a day, 3 times a week.
Just a passer-by, nor English teacher. But would like to have a try just for your reference: I think that this sentence means: to do shaping only takes you five minutes everyday and 3 times a week; or shaping can be done in just 15 minutes everyday,.... I think, here, "in" functions similarly as in a sentence like: I will be back "in" 5 minutes. Anyway, just for your consideration.