Final answer:
Jack and Sophia are experiencing the Disillusionment Stage of their marriage, which is marked by routine and a lack of active engagement, according to social studies and the concept of the family life cycle.
Step-by-step explanation:
Jack and Sophia, who have been married for 15 years and now communicate only as necessary, are experiencing the Disillusionment Stage of their marriage. This stage is characterized by feelings of stagnation or going through the motions without the energy and engagement that earlier stages of the relationship might have had. The family life cycle and its stages are a component of social studies that examines the dynamic nature of families over time.