A 15-sided figure is called a pentadecagon.
90
15
15
heptagon * * * * * No. That is a 7 sided figure. A 17 sided figure is a heptadecagon.
Pentadecagon, although most mathematicians would use "15-gon."
A ten sided figure is a decahedron.
An eight sided figure is an octagon.
Assuming the question is about a 15 sided figure rather than a 15 shaped figure, it is most commonly known as a pentadecagon, less so as a quindecagon, and even less familiarly as pentakaidecagon.
Icosagon is a 20 sided figure.
A six sided figure is called a hexagon.
a twlve sided figure is calles a pentogram