My sister's Early 2015 MacBook Air won't turn on with the power button on the keyboard or by opening it. It only turns on when connecting the charger. Before logging into the computer, the charger LED shows red, and when she logs in it shows green. The power bar at top says 100%. The System Report says that the battery is normal and can hold 6300, which is really close to the 6800 when you buy a new system. The MacBook only stays on when the charger is connected. As soon as the charger loses any kind of contact with the charge port, the macbook shuts down completely (not sleep mode, complete shutdown). As the System Report suggests, I believe this might be a shorting issue with the MagSafe IO port. Anybody have any similar issues? (We have no official retailers here so we don't trust them). I want to be able to fix it myself.
... you could try doing a 'Apple Hardware Test' or probably, with your 2015 model, an 'Apple Diagnostics Utility' to check your hardware.
Boot up while holding down the 'D' key, ... or if that doesn't work, hold down the 'Option + D' keys. Then check your hardware. Hope it helps