Centripetal acceleration is the radial component of resultant acceleration.

Referring the figure in question, radial component of the resultant acceleration,

$=15\cos 30°=15\times \frac{\sqrt{3}}{2}$

$\Rightarrow \frac{v^{ 2}}{r}=15\times \frac{\sqrt{3}}{2}$

 $\Rightarrow v=\sqrt{15\times \frac{\sqrt{3}}{2}\times 2.5}\simeq 5.7 \mathrm{m} {\mathrm{s}}^{-1}$.