I regularly make 14 inch pizzas and use my 12 inch metal peel to take them out.
On the other hand I use a wooden peel that was 16 inches until I cut down the side edges to about 15.25. This one I use to launch only. I stretch by hand and place it on the wooden peel (already has some semolina on it) and adjust it round and add toppings, shake to make sure it isn't stuck the pie may pull in a little no big issue. The cut down size is just so I do not make a pie too big for my blackstone oven pizza stone (16in). In your case it would be a way to know how big fits in the opening. Don't try to maximize too much, you may have an issue with your pie being slightly oblong when launched then turning it in the oven while cooking only to find you need to turn it again to get out the door.
Stick with the metal peel you have and get a wood one for launching, you can get a 14 inch one but the 16 is almost no extra cost and use a plane to shave down the beveled sides that you won't be using anyway if only for launch.
This is mine:https://www.amazon.com/dp/B005K8MSXE/?tag=pmak-20
I like the long handle, my forearm steadies the peel on the launch no wobble or leaning side to side.