Need help with a formula

[bryanp21]

I'm adding two cells together and multiplying by 3(=sum(a1:b1)*3), but I don't want the total to exceed 15. Is there a way to do this? Below is an example of what I'm doing.

Cell A1 has a value of 5 and cell B1 has a value of 12. I want to subtract cell A1(5) from cell B1(12), then multiply times 3.
=sum(a1:b1)*3
This will give me a value of 21, but I need the maximum value to be 15.

Can someone please help!!

Thanks