Macbook Pro Mid-2015 Backlight Burning Bright
Is it repairable?


Yes.  The backlight or the entire screen assembly can (should) be replaced.  This is something you can do yourself with a replacement LCD and the instructions from ifixit.com.  It's basically removing the back panel, disconnect the display and WiFi cables, then detaching the assembly brackets/hinges.


  is it covered under warranty?


When did you purchase it?  Within 1 year (US) it will be covered.   Is you MacBook Pro still covered under AppleCare (extended warranty)?  If not, it's likely this will be an out-of-pocket expense.

Check your Apple service coverage to verify.