XV
10 + 5 = 15
XV breaks down as X + V (X = 10, V = 5), which add up to 15.
XV breaks down as X + V (X = 10, V = 5), which add up to 15.
The number 15 is written XV in Roman numerals. Roman numerals use seven letters — I (1), V (5), X (10), L (50), C (100), D (500) and M (1000) — combined from largest to smallest, with subtractive pairs such as IV (4) and IX (9). Need another number? Use the Roman numeral converter or see the 1–100 chart.