The line has 41.4 km long (25.7 mi) with 18 stations, connects the suburbs of Shunyi District with the existing subway network at Wangjing (Line 14), Wangjing West (Line 13), Datunlu East (Line 5) and Olympic Green (Line 8). The operational sections run from the Qinghuadongluxikou in Haidian District to Fengbo in Shunyi District. Line 15 travels underground from Qinghuadongluxikou to Maquanying, and then goes above ground on an elevated track to Houshayu before returning underground and going underneath the Chaobai River to Fengbo. The elevated section is high enough to allow elevated roads to pass underneath. A major public venue on the Line 15 route is the New China International Exhibition Center (New CIEC) at the China International Exhibition Center Station. New CIEC holds the annual Beijing International Automotive Exhibition, which attracted 800,000 visitors in 2012.
During planning of Line 15, the eastern terminus was moved from Fuqian Jie to the east bank of the Chaobai River. Construction began on Phase I of Line 15 in Shunyi District on April 11, 2009. At that time, Phase I of Line 15 was only 31.15 km (19.36 mi) long with 12 stations. According to the construction schedule in 2009, the eastern-most Shunyi section of Phase I (18.5 km or 11.5 mi in length with seven stations) would be opened first on December 30, 2011. The remainder of Phase I would follow in May 2013.
The route of Line 15's Phase II has been revised several times over the years. In April 2009, Phase II plans showed the western half of Line 15 running from Xiyuan Station in Haidian District, through the campus of Tsinghua University, Zhongguancun, and the Olympic Green, and joining Phase I at Wangjing West.When track-laying began in Phase I on October 28, 2009, the schedule and alignment of Phase II underwent a major revision, with one proposal extending Line 15 westward as originally planned with additional stations and another proposal sending Line 15 southward and parallel to Line 8 to provide relief for congested Line 4 and 5. Ultimately the route west to Qinghuadongluxikou was selected and the design of Xiyuan station leaves enough space to build another platform in between Line 4 and Line 16 platform for potential Line 15 extension westward beyond Qinghuadongluxikou. Additionally the construction schedule was revised with Phase I expanded from 31 km (19 mi) and 12 stations to 38 km (24 mi) and 18 stations. Phase II plans also underwent a revision; instead of two sections, Phase II would be built and opened in three sections.
The first section of Phase I, from Wangjing West to Houshayu, opened on December 30, 2010. The second, from Houshayu to Fengbo, followed at the end of 2011. The third section, from Qinghuadongluxikou to Wangjing West, opened on December 28, 2014.
Line 15, Phase I stations, from east to west with transfers in parentheses: