$15$ At any angular speed, a certain uniform solid sphere of diameter $D$ has half as much rotational kinetic energy as a certain uniform thin$-$walled hollow sphere of the same diameter when both are spinning about an axis through their centers. If the mass of the solid sphere is $M,$ the mass of the hollow sphere is

$5/6$ M$.$

$5/3$ M$.$

$6/5$ M$.$

$2M.$

$\frac{3}{5}M.$