Final answer:
In 'Sir Gawain and the Green Knight,' the residents at Camelot Castle celebrate Christmas with a festive gathering that spans fifteen days.
Step-by-step explanation:
At the beginning of the poem Sir Gawain and the Green Knight, the residents of Camelot Castle are enjoying a holiday celebration that lasts for fifteen days. This celebration is to mark the Christmas time and is filled with feasting, merriment, and the exchange of gifts. The number of days is significant, as it represents a lengthy period where noble knights, ladies, and royalty partake in the pleasures and generosity of the season before embarking on chivalric or spiritual quests, such as the one Sir Gawain himself undertakes following the Green Knight's challenge.