The problem asks to factor the expression $ab - 3a + 15 - 5b$.

1. Problem Description

The problem asks to factor the expression $ab - 3a + 15 - 5b$.

2. Solution Steps

First, we rearrange the terms:

$ab - 3a - 5b + 15$

Now, we factor by grouping. From the first two terms, we can factor out an $a$:

$a(b - 3) - 5b + 15$

From the last two terms, we can factor out a $-5$:

$a(b - 3) - 5(b - 3)$

Now we have a common factor of $(b - 3)$:

$(b - 3)(a - 5)$

So the factored expression is $(a-5)(b-3)$.

3. Final Answer

$(a-5)(b-3)$