Question: The 15th Infantry Division was an infantry formation of the Russian Imperial Army that existed in various formations from the early 19th century until the end of World War I and the Russian Revolution which dismantled the Tsarist autocracy and led to the rise of what?

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8th Infantry Division (Russian Empire): The 8th Infantry Division (Russian: 8-я пехотная дивизия , "8-ya Pekhotnaya Diviziya") was an infantry formation of the Russian Imperial Army that existed in various formations from the early 19th century until the end of World War I and the Russian Revolution.  The division was based in Warsaw in the years leading up to 1914.  It fought in World War I and was demobilized in 1918.

7th Infantry Division (Russian Empire): The 7th Infantry Division (Russian: 7-я пехотная дивизия , "7-ya Pekhotnaya Diviziya") was an infantry formation of the Russian Imperial Army that existed in various formations from the early 19th century until the end of World War I and the Russian Revolution.  The division was based in Radom and later Voronezh in the years leading up to 1914.  It fought in World War I and was demobilized in 1918.

13th Infantry Division (Russian Empire): The 13th Infantry Division (Russian: 13-я пехотная дивизия , "13-ya Pekhotnaya Diviziya") was an infantry formation of the Russian Imperial Army that existed in various formations from the early 19th century until the end of World War I and the Russian Revolution.  The division was based in Sevastopol in the years leading up to 1914.  It fought in World War I and was demobilized in 1918.

11th Infantry Division (Russian Empire): The 11th Infantry Division (Russian: 11-я пехотная дивизия , "11-ya Pekhotnaya Diviziya") was an infantry formation of the Russian Imperial Army that existed in various formations from the early 19th century until the end of World War I and the Russian Revolution.  The division was based in Lutsk in the years leading up to 1914.  It fought in World War I and was demobilized in 1918.

12th Infantry Division (Russian Empire): The 12th Infantry Division (Russian: 12-я пехотная дивизия , "12-ya Pekhotnaya Diviziya") was an infantry formation of the Russian Imperial Army that existed in various formations from the early 19th century until the end of World War I and the Russian Revolution.  The division was based in Lutsk in the years leading up to 1914.  It fought in World War I and was demobilized in 1918.

10th Infantry Division (Russian Empire): The 10th Infantry Division (Russian: 10-я пехотная дивизия , "10-ya Pekhotnaya Diviziya") was an infantry formation of the Russian Imperial Army that existed in various formations from the early 19th century until the end of World War I and the Russian Revolution.  The division was based in Warsaw and later Nizhny Novgorod in the years leading up to 1914.  It fought in World War I and was demobilized in 1918.

15th Infantry Division (Russian Empire): The 15th Infantry Division (Russian: 15-я пехотная дивизия , "15-ya Pekhotnaya Diviziya") was an infantry formation of the Russian Imperial Army that existed in various formations from the early 19th century until the end of World War I and the Russian Revolution.  The division was based in Odessa in the years leading up to 1914.  It fought in World War I and was demobilized in 1918.

14th Infantry Division (Russian Empire): The 14th Infantry Division (Russian: 14-я пехотная дивизия , "14-ya Pekhotnaya Diviziya") was an infantry formation of the Russian Imperial Army that existed in various formations from the early 19th century until the end of World War I and the Russian Revolution.  The division was based in Kishinev in the years leading up to 1914.  It fought in World War I and was demobilized in 1918.

Russian Revolution: The Russian Revolution was a pair of revolutions in Russia in 1917 which dismantled the Tsarist autocracy and led to the rise of the Soviet Union.  The Russian Empire collapsed with the abdication of Emperor Nicholas II and the old regime was replaced by a provisional government during the first revolution of February 1917 (March in the Gregorian calendar; the older Julian calendar was in use in Russia at the time).  Alongside it arose grassroots community assemblies (called 'soviets') which contended for authority.  In the second revolution that October, the Provisional Government was toppled and all power was given to the soviets.

9th Infantry Division (Russian Empire): The 9th Infantry Division (Russian: 9-я пехотная дивизия , "9-ya Pekhotnaya Diviziya") was an infantry formation of the Russian Imperial Army that existed in various formations from the early 19th century until the end of World War I and the Russian Revolution.  The division was based in Radom and later Voronezh in the years leading up to 1914.  It fought in World War I and was demobilized in 1918.

Supporting paragraphs: 15th Infantry Division (Russian Empire) Russian Revolution
Answer: the Soviet Union