15. (6 points) There are three numbers $a, b, c$, $a \times b=24, a \times c=36, b \times c=54$, then $a+b+c=$
【Solution】Solution: Since, $(a \times b) \times(a \times c) \div(b \times c)=24 \times 36 \div 54=16$, that is $a^{2}=16$,
so $a=4$,
$$
\begin{array}{l}
b=24 \div a=6, \\
c=36 \div a=9, \\
a+b+c=4+6+9=19 ;
\end{array}
$$

Therefore, the answer is: 19 .