Consider three sets $E_1=\{1,2,3\},F_1=\{1,3,4\}$ and  $G_1=\{2,3,4,5\}$. Two elements are chosen at random, without replacement, from the set  $E_1$ and let  $S_1$ denote the set of these chosen elements. Let $E_2=E_1-S_1$ and  $F_2=F_1\cup S_1$. Now two elements are chosen at random, without replacement, from the set  $F_2$ and let $S_2$ denote the set of these chosen elements. Let  $G_2=G_1\cup S_2$. Finally, two elements are chosen at random, without replacement, from the set $G_2$ and let  $S_3$ denote the set of these chosen elements. Let  $E_3=E_2\cup S_3$. Given that  $E_1=E_3$, let p be the conditional probability of the event  $S_1=\{2,3\}$. Then the value of 15 p is