I'm on my way to Stansted airport and I realized I forgot to print my boarding pass and I also can't use the mobile BP as I'm a non-EU citizen. Would Ryanair actually charge me 15 pounds to get the BP?
Completely depends on the agent.
When I was in London in January, I failed to find anywhere to print it, and when I got to Stansted, one agent did want to charge me 15 quid. Discretely went to another agent, who printed it for free.
Don't know if being EEA or non-EEA matters, but it could (with EEA pax being treated more strictly, seeing as non-EEA pax have to visit the counter anyway).