15. (5 points) It is known that Xiaoming's father and mother are of different ages, and the difference in their ages does not exceed 10 years. If last year, this year, and next year, both father and mother's ages are integer multiples of Xiaoming's age, then Xiaoming is $\qquad$ years old this year.
【Answer】Solution: Since the age difference between the three people is constant,
and the ages of the three people over these three years form three sets of consecutive natural numbers,
the age difference between the parents does not exceed 10 years, and within 10, only 6 has three consecutive divisors, which are $1, 2, 3$. Therefore, Xiaoming is 2 years old this year, and the age difference between the parents is 6 years.

Therefore, the answer is: 2.