15. Every book has an international book number:

ABCDEFGHIJ
where $A B C D E F G H I$ are composed of nine digits, and $J$ is the check digit.
$$
\text { Let } \begin{aligned}
S= & 10 A+9 B+8 C+7 D+6 E+5 F \\
& +4 G+3 H+2 I,
\end{aligned}
$$
$r$ is the remainder when $S$ is divided by 11. If $r$ is not 0 or 1, then $J=11-r$ (if $r=0$, then $J=0$; if $r=1$, then $J$ is represented by $x$). If a book's number is $962 y 707015$, then $y=$ $\qquad$
$$
\text { 15. } \begin{aligned}
S=9 \times 10 & +6 \times 9+2 \times 8+y \times 7+7 \times 6 \\
& +0 \times 5+7 \times 4+0 \times 3+1 \times 2
\end{aligned}
$$
$\therefore S$ the remainder when divided by 11 is equal to the remainder when $7 y+1$ is divided by 11.

From the check digit, we know that the remainder when $S$ is divided by 11 is 11 $-5=6$, so the remainder when $7 y$ is divided by 11 is $6-1=5$. Therefore, $y$ $=7$.