Ok...I can't take complete credit for this fix as this has been done by a couple of members here, but I can take full credit for the way I did it.
For those who have considered lifting or leveling your 2015 Sierra Denali and have had worries about the magnetic ride control affecting the ride, the solution is within.
There is 2 ways to do this. 1 way is to fabricate a bracket with some flat stock, drill 2 holes, connect the bottom hole in the fabricated bracket to the original bracket that is attached to the upper control arm, and then connect the upper hole in the fabricated bracket to the MRC rod. If you search, you can find these photos or maybe someone who has done it like this will chime in and provide pics.
Now, if you want an easier way or just don't have the tools to cut, drill, etc. and fabricate a bracket, a longer metric bolt and a handful of washers net the same result. I have the tools and material to fabricate said bracket, but I wanted go this route as it was trial and error for me. This is due to not knowing the starting position before installing the kit. Sadly, I didn't even know the truck had MRC before installing the kit. It wasn't till I experienced the extremely poor ride after the install that I figured out that it had it.
Anyhow, I would highly suggest you figuring out a way to measure and pinpoint a "home" position for the MRC rod and then after the kit, you can determine how much you need to move the MRC rod to put it back where it started. If you're like me and you never started out with a home position, you can just add washers until you get the desired ride you want. For me, it was a total of 18 washers that equated to 1" in length. I taped them for the ease of installation.
As you can see from the pic, instead of raising the MRC rod by fabricating a bracket, I raised it with washers on the bracket that is affixed to the upper control arm. Hope this helps!