How long do your batteries last at -15 degrees?
Very cool shots. I've found that if I focus to infinity, then back off just a hair, the shot is in focus. If I try and just go to infinity, then they're usually a tad out of focus.
I've also found that having something in the foreground like your first image usually makes the image a bit more interesting. I wasted a ton of shots one night with everything in focus and nothing blurred. Problem was it was just a bunch of stars and I didnt find anything interesting in the images. i.e. no good constelations or any shooting stars.
I also have a headlamp that has a red filter, so I can adjust any of the camera settings and I dont ruin my night vision. It works great and doesnt use up battery life on the camera by turning on the backlight on the LCD.