8. Given the equation of circle $\odot C$ is $x^{2}+y^{2}-8 x+15=0$. If there exists at least one point on the line $y=k x-2(k \in \mathbf{R})$ such that the circle with this point as its center and 1 as its radius has a common point with $\odot C$, then the maximum value of $k$ is $\qquad$.