While I haven't tried the Taste of Home recipe, I make a very similar cake called Texas Sheet Cake (and I've seen it called many other names). That 15 x 10 x 1" jelly roll pan is pretty big - this cake is not very high like a cake baked in a 13 x 9 x 2" pan. More like the thickness of a cake-like brownie. I bake mine for 20 min. and it's about right. Dry ingredients of your recipe & mine are pretty much the same. That's the long way of saying I think the 15-20 min. is correct if you use the pan size they suggest.