How many letters does the top answer for “a plane figure with fifteen angles, and consequently fifteen sides.” have?

The most common answer is quindecagon (11 letters).

Crossword clue: a plane figure with fifteen angles, and consequently fifteen sides.

1 answer found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

quindecagon 11 letters web-def

A plane figure with fifteen angles, and consequently fifteen sides.

a plane figure of eleven sides and angles. 57% similar → endecagon

a plane figure of eleven sides and eleven angles. 57% similar → hendecagon