11x 15 vs. 9x13

I have a recipe for zucchini cake that calls for an 11x15 pan. I don't have one. I wonder if a 9x 13 would work. Just be thicker, no? Maybe longer bake time?

11x15=165 sqin
9x13=117 sqin
the smaller pan is 70% the size of the larger (117/165=.7)
multiply all the ingredients by .7 and the cake should come out just fine as long as you send me a slice.

Ken's suggestion should work fine.

The problem would lie in using the original recipe for a smaller square inch size dish.

Since you would be using only 70% of the ingredients, the cake will still be the same thickness.
I would check it several times before the recommended cook time.
Even though it is the same thickness, the volume will be less, so it might cook quicker.

Recipes are like "Stop" signs in Italy: they are only suggestions.

If a muffin pan is handy, whip up the recipe, fill the small pan, then make muffins with the excess.