Step 1: Background on Planning Commission.
Before NITI Aayog, India had the Planning Commission, which was set up in 1950 to formulate five-year plans for the country.
Step 2: Formation of NITI Aayog.
The Planning Commission was replaced by NITI Aayog on January 1, 2015. NITI stands for \textit{National Institution for Transforming India}.
Step 3: Objective of NITI Aayog.
It focuses on cooperative federalism, policy inputs, and long-term development strategies.
Step 4: Conclusion.
Thus, NITI Aayog was set up in 2015, making option (3) correct.