SR15B stands for "SM Rookies 2015 Boys", a name used for S.M. Entertainment's boys' pre-debut training team of 2015. As of 2024, it has been used only for one recording, "Switch", a song originally performed in the SM Rookies Show in 2015. The song was recorded in 2015, and put as part of the NCT 127's debut mini-album in 2016 since a lot of the graduated members were in the group. The line-up on the recording is: Johnny (쟈니), (태용), Hansol (한솔), Ten (텐), Jeno (제노), Jaemin (재민), Jisung (지성), Taeil (태일), Yuta (유타), (도영), Jaehyun (재현), Mark (마크), and Haechan (해찬).