def METHOD_NAME(conference: Conference) -> Set[int]:
    cache_key = f"conference:{conference.id}:speakers_user_ids"
    if cache.has_key(cache_key):
        return cache.get(cache_key)
    submission_speakers = list(
        ScheduleItem.objects.filter(
            conference=conference,
        )
        .values_list(
            "submission__speaker_id",
            flat=True,
        )
        .distinct()
    )
    additional_speakers = list(
        ScheduleItem.objects.filter(
            conference=conference, additional_speakers__user_id__isnull=False
        )
        .values_list("additional_speakers__user_id", flat=True)
        .distinct()
    )
    items = set(submission_speakers + additional_speakers)
    cache.set(cache_key, items, timeout=60 * 60 * 24 * 2)
    return items