You have 1/2 of a ring and two long ends:
Ring formula: (diameter (1mm) + sheet thickness (1mm)) x pi = 2 x 3.14159 = ~6.283mm / 2 since you only need half (as the bend is only 1/2 of the "ring")= ~3.142mm
Plus the two tails: 2 x total length (15mm) - the distance taken by the bend, which in this case (as you can see in the diagram) is 1.5mm (1 radius + 1 sheet thickness): 2 x 13.5mm = 27mm
So I would try something like 30.15mm in copper and see if that's right (because I could be wrong, as I'm away from my bench and can't test this myself). If so, you should be able to apply this formula to any this shape with different values for overall length, bend diameter and metal thickness.
Hope this works for you!