The growth of the Web and other Big Data sources lead to important performance problems for large-scale and distributed information retrieval (IR) systems. The scalability and efficiency of such IR systems have an impact on their effectiveness, eventually affecting the experience of their users and monetization as well. Consequently, scalability and efficiency in the context of retrieval systems continue to be an important topic in IR research. The LSDS-IR'15 workshop will provide space for researchers to discuss such problems and to define new directions for the work on information retrieval in the modern Big Data era. As in previous years, we expect to bring together information retrieval practitioners from the industry, as well as academic researchers concerned with efficient and distributed IR systems.