Leon mk3 2013 fr - ignition system faulty

[Esztu]

hello everyone we have a little trouble with our beloved Leon, just in the middle of a 2000 km trip, the engine won't turn off when the key is turned, only when removed.
OBD eleven says terminal 15 error. Are we going to make it home? Is it just a relay/ fuse swap or something big?
I mean we're glad we can start and stop the car, just worried it's getting worse with time.
Thanks for any input