The Voigtlander 15mm lens has an angle of view of approximately 110° on a full frame camera, but the Leica M8 is an APS-H format (sensor size approximately 27.0 x 18.0mm), in which case the angle of view of the 15mm lens will be slightly less than the full frame 110°.

The Leica M8 sensor has a diagonal length of approx. 32.5 mm, which corresponds to an angle of view of approx. 83°.

Formula for calculating the angle of view.

The formula for calculating the angle of view is: θ = 2 arctan(d / (2f))
In this formula:
θ represents the angle of view.
d stands for the diagonal length of the sensor.
f is the focal length of the lens.