I would like to ask for help on a method to derive a desired angle.

I would like to have the angle to cut the bottom of this cylinder so that it can be placed flat and have it angled 60 degrees to the side and 15 degrees forward..

In this file I rotated the cylinder 60 to the side then 15 forward and cut it off to reveal the angle, however I realized that after I made the second rotation, this changed the first 60 angle I made....

Can anyone help me with a method/formula to end up with the angle cut I need to generate a 60/15 here?

Much appreciated... file attached.