To deepen our understanding of star-forming properties, we studied a massive protocluster IRAS 15596-5301 (I15596) using ALMA 870 μm and 3 mm data. High-resolution 870 μm data reveal 34 dense cores, including three hot molecular cores, with subsequent line surveys detecting 22 molecular species toward them. Two velocity components (I15596-red/I15596-blue) were found in the averaged H13CO+(1–0) spectrum, and two filaments were identified from velocity-resolved integrated intensity maps. A spatial overlap between the two filaments was observed, and this overlapping region exhibits a distinct bridge-shaped feature in the position–velocity diagram constructed along the entire filamentary structures. Combined with the reduced H13CO+/HCO+ ratio in the overlapping region and the three-dimensional position-position–velocity cube data, we conclude that a non-head-on collision occurs between the edges of the two filamentary structures in I15596. Cluster analysis demonstrates that clusters located in the collision region host more evolved chemical rich dense cores than their counterparts in other regions. Our results thus indicate that star formation in I15596 is triggered or accelerated by a mild non-head-on collision between two filaments.