How do stroller miles count?

These days I've been racking up lots of miles with the jogging stroller. My husband has been traveling for nearly 2 weeks and it's the dog and kids and stroller, or no run at all. Living on a very hilly road these runs are kicking my butt. I figure there is about 60lb of kids and equipment that I am pushing, plus wrangling 80lb of dog.

Needless to say, these runs are slow. Nor are they long. In my pre-kid days, I believe the term would be junk miles. Normally junk miles wouldn't bother me, but I'm 9 weeks out from the Grand Cayman Half Marathon, and I need to be logging better quality runs.

Runners World had a formula - very cheeky and 100% made up - that during pregnancy a preggo mile equalled 1.5 miles. Should stroller miles be counted differently? Should my hilly 8k tonight really be 134k - taking hills, kids, snacks and dog wrangling into consideration?

I've been running long enough to know that running slow in training translates into running slow on race day. What are some ways I can pack some speed into my stroller runs?