The correct exponential equation that models the population \( y \) after \( x \) years, given that the population declines at a rate of 2% each year, is:
\[ y = 15,000 \cdot (0.98)^x \]
This is because a decline of 2% means that each year, 98% of the population remains, which is represented as \( 0.98 \).
So, the response is:
y = 15,000 ⋅ (0.98)^x