It was discovered by Jean-Dominique Maraldi in 1746 and included in Charles Messier's catalogue of comet-like objects in 1764.

[citation needed] At an estimated 12.5±1.3 billion years old, it is one of the oldest known globular clusters.

[11] It has an absolute magnitude of −9.2, which translates to a total luminosity of 360,000 times that of the Sun.

[15] At magnitude 6.2, M15 approaches naked eye visibility under good conditions and can be observed with binoculars or a small telescope, appearing as a fuzzy star.

The cluster appears 18 arc minutes in size (three tenths of a degree across).