This is a FYI post in case it happens to any one else, you'll know what the problem might be.

I bought my 2015 is350 AWD fsport in august 2015. Its a fairly brand new car. Currently have 14.5k miles on it. last month, the steering wheel started to vibrate subtly when I was going over 50mph and then braking. The vibration only happened when i broke and slowly down to 40-45mph then stopped. it would only do it ever so slightly between 40-45mph. It wasn't bad but I noticed it. I brought it to the dealer and they decided to resurface all 4 rotors to see if that fixes it. my front brakes were at 7mm and rears were at 8mm. First they resurfaced the front and road tested it. there was slight vibration from the rear so then resurfaced the rears too. I got the car back yesterday and the problem is gone. back to smooth braking. I hope this helps someone in the future.

 

Thanks, will keep an eye out for this issue! Sounds pretty annoying but at least fairly easy to fix.