\[\boxed{\mathbf{402}.}\]
\[15\ \frac{км}{ч} = 15 \cdot 1000\ :3600 =\]
\[= 15\ 000\ :3600 = 150\ :36 =\]
\[= \frac{150}{36} = \frac{50}{12} =\]
\[= 4\frac{2}{12} = 4\frac{1}{6}\ \frac{м}{с}.\]