How old children can Canadian marriage immigrants take care of?

Children under 22 can (provided they are not married and have no job). Children over the age of 22 can emigrate with their parents before the age of 26 if they can prove that they are studying full-time, unemployed and unmarried.

Your child is only 15 years old, which is certainly possible, but remember to need the written consent (and notarization) of the child's biological father!