Could be a couple things...I also have a 2015 450i, so I have had minor steering issues as well. First thing to check is ball on the steering arm where the tie rod attaches, they can come loose, but there is a cotter key so they cant fall out. They also wear from the heavy plow, I have replaced mine (3k miles) ...If ball joint is tight then a front end alignment may be needed. I use n 8' long straight edge to align front and back wheels, I set mine to 1/8" or less toe in on each side. Look at tire wear...badly worn or uneven worn tires can cause wobble, especially on pavement. Hpoe these ideas help your issues..by the way, I can steer my 450i with one hand in 4wd and it tracks straight as an arrow on the road, dont know why I would ever need power steering?? And I am 72 yrs old!!