One problem related to check engine light on has been reported for the 2015 BMW X5. The most recently reported issues are listed below.
2015 X5 diesel had its check engine light illuminate @ ~85,650 miles while driving normally at surface street speeds. Did not notice any driveability/performance issues, but took vehicle to dealer within a week. Check engine light would go on and off for the week leading up to dropping off. Dealer diagnosed as failure of 2 injectors. Cylinders 1 and 2. Paid to have vehicle repaired and appears to be driving normally and no return of cel as of yet (about 50 miles). BMW has an extended 120,000 mile warranty (sib 01 09 19) on injectors for the model year 2016 and 2017 X5 diesel with the same engine and same injectors as well as various my 2015, 2016, and 2017 diesel vehicles. Coverage should be extended to model year 2015 X5 as well as believe it likely the 4 remaining original injectors will fail as well. Hopefully BMW will add extended warranty of the injectors to the 2015 my X5 diesels which would allow for reimbursement.