Josiah is 15 x 3 = <<15*3=45>>45 years old now.
In three years, Josiah will be 45 + 3 = <<45+3=48>>48 years old.
Hans will be 15 + 3 = <<15+3=18>>18 years old in three years.
So, the sum of their ages in three years is 48 + 18 = <<48+18=66>>66 years old.
#### 66