Porcelain is helpful in mechanical modeling for smoothing three and five point patches (it also does a great job on cleaning up corners). It's no substitute for a good spline layout, but it will help get rid of some concave areas created from non four-pointers and some overall smoothing...it's slight, but noticeable. When I apply Porcelain, I don't adjust the "Normal weight"...I haven't come across splineage that would require anything more than a slight tweak from the material.
Yessir, Porcelain works in v15.
I don't use Porcelain on organic models, although I know some people do. It would be an extremely rare case for me to use it on anything organic...maybe on a set of horns or teeth, but not on any fleshy parts.
The biggest difference in the way I model mechanical objects as opposed to organic objects is that I peak almost everything when mechanical modeling (tweaking the bias' like crazy) and I don't touch the bias' except in very rare cases on organic objects. I also bevel everything I can think of on mechanical objects...it makes a big difference.
Here's a quick model with two rectangular objects, one is beveled and one is not. Even in a quick render, the difference is very noticeable. If you apply Porcelain to the beveled object, you'll see a very slight improvement on some of the edges. I actually used a resized version of this beveled example for the doors and lids on the dumpster.
Hope that helps, Matt.
beveling_example.zip