Originally Posted by 2F/2F
I'd think the closest common focal length would be a 135mm, not a 180mm. 135mm is 10 percent shorter than 150mm, and 180mm is 20 percent longer than 150mm.
If 15 degrees over the diagonal is needed, the calculator says about 163 mm.
A 150 mm lens on 35 mm format has a diagonal angle of view of 16.4 degrees.