To factor the expression \( 5m - 15 \), we can look for the greatest common factor (GCF) of the two terms.
The GCF of \( 5m \) and \( 15 \) is \( 5 \).
Now, we can factor out \( 5 \):
\[ 5m - 15 = 5(m - 3) \]
So, the factored form of the expression \( 5m - 15 \) is:
\[ 5(m - 3) \]