Flat Rate UPS shipping

Is there a way to set up a flat rate of $15 UPS shipping on all orders?

Thank you kindly in advance for your help.

I'm not sure what you want to do.

If you want to have a flat shipping fee, you can create a manual shipping method via the menu System>Shipping methods.

If you want to add a flat shipping fee on top of the UPS shipping fee which is dynamically calculated, you can fill the "handling fee" option of the UPS shipping plugin.