Answer
$15c$
Work Step by Step
In general, the words "product of" and "times" represents the mathematical operation for multiplication. The product of numerical expression $15$ and algebraic expression $c$ indicates that the variable $c$ is increased itself by $15$times.
The multiplication operation is indicated by symbol "$\times$" or by a dot in between or by placing each expression in brackets. Therefore, product of $15$ and $c$ is represented as $15\cdot c$, $15\times c$ or $15 (c)$.
Since, the product involves only a single variable, it is best represented as $15c$.