To construct the function \( g(x) \) from \( f(x) = \log_8 x \), we first reflect it across the y-axis, giving us \( f(-x) = \log_8(-x) \). Next, we vertically shrink it by a factor of 15 to obtain \( \frac{1}{15} \log_8(-x) \), and finally, we shift it down 7 units, resulting in \( g(x) = \frac{1}{15} \log_8(-x) - 7 \).
Thus, the function is \( g(x) = \frac{1}{15} \log_8(-x) - 7 \).