One problem related to headlight switch has been reported for the 2015 Chevrolet Impala. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2015 Chevrolet Impala based on all problems reported for the 2015 Impala.
The design of the headlights is faulty. The reflectors behind the bulbs do not project sufficient illumination of the road ahead, nor does it illuminate the left and right corners. I estimate that the very dim lights are good for 30-ft ahead at most, and they are so dim that they are almost useless when driving in am and pm hours. Switching to high-beams barely makes a difference. In fact, I always drive with the high beams on when driving in the dark, and have never had an oncoming vehicle flash its lights at me in attempt to get me to swiych to the low-beams. Further, turning corners in the dark is dangerous, as there is virtually no illumination of the corners by the headlights. All of this is exacerbated significantly when the pavement is wet and when it's raining. I suggest that you take a test drive in one of these vehicles, in " country" environments that are not lit by street lights. Do it again on similar roads when it's raining. Search google "impala poor headlight design" and you will find that this hazard is discussed in several forums and reviews for 2015 through 2018 Impalas. It boggles the mind to know that general motors has allowed this safety issue to be perpetuated through 4 Impala model years.