The only reason for a difference in lines/mm would be a difference in the lens design. The degrading effects of diffraction on lens resolution would be virtually identical between the two lenses you mentioned in your example at their respective apertures (300 @45 and 150@22).
Originally Posted by Tom Duffy
As to your second question, there once again it would depend on how much you intended to enlarge the resulting negative. If you accept the same 'circle of confusion' parameter for both lenses, then the depth of field of a 150mm at f/22 would be identical to a 300mm at f/45. As others have pointed out, it will also depend on how large your final intended print will be and what viewing distance you expect the viewer to maintain.