To find the average growth of the town's population over the next 5 years, we first need to determine the annual growth rate based on the growth in the last 2 years.
The town has grown by 600 people in 2 years, so the average annual growth is:
\[ \text{Annual Growth} = \frac{600 \text{ people}}{2 \text{ years}} = 300 \text{ people per year} \]
Now, to find the total growth over 5 years, we can multiply the annual growth by 5:
\[ \text{Growth in 5 years} = 300 \text{ people/year} \times 5 \text{ years} = 1500 \text{ people} \]
Therefore, the answer is 1,500 people.