activating the JR card

Konnichiwa Danielsan - we have 4x15-day JR passes.

We arrive on 16 Dec at Narita and will activate our passes at the airport and use it to get to our hotel in Shinjuku. Based on the 15 days am I correct in assuming that we can use our JR pass until our last day in Japan on 30/12 (departure Narita 19:20)?

Arigatou Gozaimasu,

Yash