I've done 15+ mile hikes with the K-1. For reference, I'm 52 years old with good legs, bad shoulders, and no major health issues.
I usually don't bring a tripod when I'm hiking that far. If I'm going into dark spots like caves or abandoned buildings, or expect to do a time lapse, I'll bring my Manfrotto 190CXPRO3 tripod attached to my backpack, or a smaller flimsier tripod inside the backpack.
My usual lens setup is the 28-105 on the K-1. That lens is light enough that I can keep the camera strapped to my chest for easy access (like in the advertisement photo below). If I'm on very rough ground, though, the camera goes into my bag because a forward fall would be horrible for my camera and my ribs.
Depending on what I expect on the hike, I might add the 15-30 plus 55-300, or just a Sigma 50-500 by itself when my main goal is wildlife.