Complex sentence: In January 2015, Mills stopped modelling to focus on his acting career which kicked off in November 2015, when he started filming Chris Wright's Thriller film, "The Waterboatman", in which Mills stared as Neil, a failed musician.
Split into simpler sentences: In January 2015, Mills stopped modelling to focus on his acting career. Which kicked off in November 2015, when he started filming Chris Wright's Thriller film,' The Waterboatman', in which Mills stared as Neil, a failed musician.