Many 2015 models suffer from the anti-reflective coating peeling off. Check for splotchy or stained-looking marks on the display.
Since this model is now over a decade old, you need to check these specific areas before purchasing: how to buy macbook pro 2015
Test every single key. A common failure in the 13-inch model is the trackpad cable , which can cause both the trackpad and keyboard to stop responding. Many 2015 models suffer from the anti-reflective coating