This may seem like a silly question, but this is the second time I've baked a 12x15 sheet cake, did two of them to stack on top of each other. I'm sitting here trying to figure out once I put the icing on the first layer how do I put the top cake on without it breaking? With an 8" it's easy peasy, but this is so big that I cannot just pick it up with my hands without it breaking in two. I really need help on this one. Thank you!

You put it on a cardboard or a rimless cookie sheet and slide it off onto the bottom layer.

Thanks Leah, I was thinking that, but wasn't quite sure if it would work out right. Thank you!

Freeze them and they handle really well.

I second freezing the cake. I generally use spatulas as lifters and I can easily move a 12 x 18 layer around and get it placed exactly where I want it while it's frozen. Sliding the spatulas out from between the layers is easier than sliding a layer of cake off a board and getting it to land in the right place.

I have a large piece of cardboard that I covered with freezer paper. I use this for lifting difficult cake layers and also large layers of rolled out fondant. Freezer paper is like a heavy duty wax paper so it can be wiped of and reused.