Try what you've already got. It can't hurt.  If you feel the need to try something else go right ahead. Enjoy your MG-1s. In 1976 they were my introduction to the "high end". I haven't looked back since.

FWIW: I use DH Labs Q-10 Signature speaker cable.

That 15-gauge wire is too small.

I suggest that you use 12 gauge wire.

Monoprice 12 gauge speaker wire is $30 for a 100-foot spool.

The stock number is Monoprice #2789.

15 gauge wire may be fine to use, but who could say one way or the other, without knowing the length of the wire and the maximum allowed resistance target.

There are many charts to be found by searching "speaker wire gauge". Check this out.

http://www.crutchfield.com/S-DELkjA2YaQZ/learn/learningcenter/home/speakers_wire.html

As for radioshack, some people might think their wire is too inexpensive to sound good, but I would try it.