Cramer-Rao bound times 15

Let $X_1, \dots, X_5$ be a random sample from $N(\theta, 6)$, where $\theta \in \mathbb{R}$, and let $c(\theta)$ be the Cramer-Rao lower bound for the variances of unbiased estimators of $\theta$ based on the above sample. Then $15 \inf_{\theta \in \mathbb{R}} c(\theta)$ equals __________ (answer in integer).