As its title suggests, the film is based on the first Mobile Suit Gundam TV anime's 15th episode of the same name, which was aired in Japan on July 14, 1979. The episode depicted the melancholy of war through the interaction of the protagonist, Amuro Ray, with Doan, a deserter from the Zeon army. The film version tells that story again, using the latest visual technology, including CGI.
The first series' character designer / chief animation director Yoshikazu Yasuhiko serves as director. While the clip introduces Amuro Ray in the cockpit of RX78-2 Gundam, the voice of the character cannot be confirmed. So at this point, we don't know how many of the original voice cast members will or won't be returning.