To me "from 15-20" implies you are starting at a number between 15 and 20. Not that the entire range is 15 to 20.
And yes there is also the problem of inclusive or exclusive.
Interesting. To me, "a number from A to B" is inclusive because "from" implies belonging, making the bounds at least [A,B). The "to", to me, implies the bounds on A apply to the bounds on B. So that would make it inclusive on both edges.