I am also wondering how one could walk at 3 mph.

I use this pace converter: http://www.runningforfitness.org/calc/convert.php The "starting pace" for my beginner's group equals 5 mph, but that probably means running at about 6.5 mph and then walking for one minute at 4 mph here and there.

I suggest letting go of advice on speed and just doing what feels right. I wouldn't worry about running too fast!! Especially not if you're taking walking breaks.

Enjoy! And report!!