the wilton sports ball pan says it serves 12. i need to make two half-round cakes for someone who needs to feed 15 people. can this cake stretch to serve 15? how could i bump up the servings by just a small amount like that?

You really can't I would probably make coordinating cupcakes to make up the difference. If you use an extender recipe like Wasc then you have a little extra batter anyway so the cupcakes would be an easy addition.

If you want to keep the design of the cake then your clients choice is 12 servings and cut smaller than normal slices. Or you can bake 2 six inch rounds and place one under each 1/2 but that basically doubles your servings to 24. Which would double the cost to the client.

Thank you so much! Coordinating cupcakes is a great idea.