Taken from the Agile 2015 page:
Stalwarts bridges the gap between introductory sessions and advanced sessions, focusing on specific, real-time questions, challenges, dilemmas, and issues that attendees bring to the conference. Experienced agile/lean practitioners - folks who have been in the trenches for many years, who wrote the books, maintained useful blogs, created the methods and approaches, coached the coaches - show up for a focused conversation with you in an open fishbowl format. There will be no prepared slides or talks, just spontaneous dialogue with you about your real challenges and questions.
The topic for Bas and Craig will be: Scaling Agile with LeSS.