If I read between the lines, here's how I see the space. You said 15" clearance on top and left side, 24" on bottom and I assume the right side is open. Most folks can reach 30"-36", so you could probably add up to 24" to the bench work at the top of the aisle. Depending on how open the right side is, you could also add up to 24" to that side. If the room allows, you could even move the aisle and right side up to 24" to the right giving you even more surface area. I should point out that a 24" aisle can get tight if you have 2 or more people trying to move around, so you might want to increase it to 30"-36". I agree with Jan that knowing more about the whole room would be helpful.
