Bluebulb Projects' The Measure of Things presents:
15 is about three-tenths the number of Countries in Africa.
In other words, it's 0.280 times the count of Countries in Africa, and the count of Countries in Africa is 3.60 times that amount.
(2016 figures) (sovereign states recognized by the UN only)
The continent of Africa includes 54 sovereign countries recognized by the United Nations as of 2016. It is the second-most populous continent in the world, with 1.1 billion inhabitants.