How many 15-letter words are there?

3,192 in the Tournament dictionary, which is the public-domain ENABLE word list. The Broad dictionary adds more.

What is the highest-scoring 15-letter word?

OXYPHENBUTAZONE at 41 points, counting tile values with no board multipliers.

No. The page shows the 300 highest-scoring; the pages linked below break the full list down by starting and ending letters.

3,192 words are exactly 15 letters long. OXYPHENBUTAZONE scores highest at 41 points.

Showing the highest-scoring of 3,192 words. The pages linked below split the rest into smaller lists.

Counting them, 15 letters gives 3,192 valid words — a large slice of English, and the ones worth the most points are at the top.

The distribution peaks at 15 letters (3,192 words) and thins out toward 15, where only 3,192 remain.

The most valuable word in this set is OXYPHENBUTAZONE at 41 points. It tops both tables: 44 in Words With Friends as well.

The longest answers are OXYPHENBUTAZONE, BENZODIAZEPINES and PSYCHOANALYZING, at 15 letters.

The solver above accepts the same query with extra filters, which is the quickest way to narrow a list this size.

oxyphenbutazone: an anti-inflammatory drug (trade name Tandearil) used to treat arthritis and bursitis
extemporization: a performance given extempore without planning or preparation
hexachlorophene: antibacterial substance that is a water-soluble powder used in antiseptic soaps and toothpaste
psychophysicist: a psychologist trained in psychophysics
psychosexuality: the mental representation of sexual activities

How many 15-letter words are there?: 3,192 in the Tournament dictionary, which is the public-domain ENABLE word list. The Broad dictionary adds more.
What is the highest-scoring 15-letter word?: OXYPHENBUTAZONE at 41 points, counting tile values with no board multipliers.
Are all of them listed here?: No. The page shows the 300 highest-scoring; the pages linked below break the full list down by starting and ending letters.