Well,  I followed your advice  and played a little bit with the settings. Compared with your recommendations, the number of shadow samples was indeed high (16). Cutting this number down to 2 did give a speed increase by a factor of something like 8 (half an hour instead of 4 hours), but an unacceptable loss in quality, skin textures degrading to what at best is a very serious skin disease, especially where the light 'strikes' the skin surface. 
Maybe it disapears at 4 or 8 shadow samples, but boosting up render times again.

Anyway, thanks for the advice. I may have a way to cut render time by a factor or two, which gives me time to walk the dog and be social with my wife. ;=)