I don't know much about running shoes, but I've got a buddy who doesn't use hiking shoes (low-top boots) - instead, he uses trail running shoes, which are lighter than hiking shoes. He carries a 25 pound load.
What I might suggest is this: load up your pack with the 22-28 pound load you're planning to carry, and go take a 5 or 10 mile day-hike at a local park, using you running shoes. You'll quickly find out not only whether they're supportive enough for the load, but also whether the tread is sufficiently "grippy" to give you enough traction on the trail. (If possible, pick a day when the trail is a little wet; you need enough traction that you're not constantly slipping around, though the occasional slip is unavoidable.)
If the running shoes work, go with them - they're already broken in and, I assume, comfortable. If not, get shoes or boots.
So, which - shoes or boots? That depends a lot on what your future loads look like. Is the decrease a permanent thing (due to changes to lighter fear and/or less gear) or is it a one-trip-only change? If you're going to be carrying the heavier load after this one lightweight trip, and boots work for you, I'd stick with boots. If you're making a permanent change to lighter loads, give the shoes a try. (I usually carry about 20 pounds for a weekend, 25 for a week, and trail shoes - low top boots - work great for me.)