Heinrich XV, Prince Reuss of Greiz was the fourth of six sons born into the reigning family of the Principality of Reuss. At the age of fifteen he joined the army of the Habsburg monarchy and later fought against Ottoman Turkey. During the French Revolutionary Wars he became a general officer and saw extensive service. He commanded a corps during the Napoleonic Wars. From 1801 until his death, he was Proprietor (Inhaber) of an Austrian infantry regiment.

In the siege of Belgrade a Habsburg Austrian army led by Feldmarschall Ernst Gideon von Laudon besieged an Ottoman Turkish force under Osman Pasha in the fortress of Belgrade. After a three-week leaguer, the Austrians forced the surrender of the fortress. During the campaign which was part of the Austro-Turkish War, the Austrian army was greatly hampered by illness. Austria held the city until 1791 when it handed Belgrade back to the Ottomans according to the terms of the peace treaty. Several Austrian soldiers who distinguished themselves during the siege later held important commands in the subsequent French Revolutionary Wars and Napoleonic Wars. Belgrade is the capital of modern Serbia.