fünftzehnte
Fünftzehnte is a form that is not recognized as standard German. It is generally considered a misspelling or typographical error for fünfzehnte, which denotes the fifteenth element in a sequence. In contemporary German, the ordinal for the number fifteen is formed from the base fünfzehn with the appropriate ordinal ending, and fünfzehnte is the form that appears in dictionaries and style guidance.
The appearance of fünfte? and fünftzehnte is typically limited to nonstandard writing, typographical slips, or historical
Etymologically, the intended root is fünfzehn (fifteen), with the standard ordinal suffix -te, yielding fünfzehnte. Spelling
In summary, fünftzehnte has no separate status in modern German. It is best understood as a nonstandard