Thus far the only two issues, I've had with my 2015 X5M was a bad HVAC blower motor, and rear air bags. I changed the voltage regulator as a preventative measure. Other than that, this vehicle has been flawless. Based on my experience, I would recommend buying one.
But, you need to allocate money on preventative maintenance. If your not willing to spend $$$$, then this isn't the vehicle for you.