Although I've never heard of any benefits of having grommets above centre, I fail to see any reason to disagree.  However, I can tell you where my snares' grommets are.  Because the bead is centred, only the Supraphonic and contemporary Black Beauty snares have grommets above centre out of the nine that I now own.  In actuality, the Radio King's grommet is a bit off-center.

Hope you track down that elusive 15" tom—completing the set would give your "poor man's Octaplus" a killer look and sound. Good luck hunting!

If you can't find a 15'' tom, you can buy a 16'' tom and shorten the shell + replace the hoop to make it 15'' (only do this if you have experience or know a shell maker).