fifteen vs large integer

fifteen and large integer both are nouns.

Word	Noun	Adjective	Verb	Adverb
fifteen	Yes	Yes	No	No
large integer	Yes	No	No	No

As nouns, large integer is a hypernym of fifteen; that is, large integer is a word with a broader meaning than fifteen:

fifteen (noun)	large integer (noun)
the cardinal number that is the sum of fourteen and one	an integer equal to or greater than ten

fifteen (adjective)	large integer (adjective)
being one more than fourteen