Tell me about the most complex program you have run.
Whether you can communicate scope at the right altitude and separate your contribution from the teams' delivery. Interviewers also listen for what made it complex: interdependency and ambiguity are interesting, headcount alone is not.
Open with the scope in numbers: workstreams, teams, functions, duration, and budget if shareable. Name the strategic goal in one sentence, then spend most of your time on the one or two mechanisms you built that made it manageable, the hardest moment, and the outcome against the committed plan. Keep it under three minutes and let the interviewer pull threads; the follow-up questions are where you prove the story is yours.