"15" is a number, which makes it a noun. Nouns do not have tenses, verbs have tenses.
The past tense is "hunted"
The past tense is "flowed.
The past tense of can is could.
Simple past tense. Past perfect tense. Past perfect continuous tense. Past continuous tense.
Played is the past tense of play.
raised IS the past tense of raise
that is the past tense
Have is present tense. The past tense is had.
The past tense of teach is taught.
The past tense of steal is stole, and the past tense of meet is met.
The past tense of hear is heard.
Lost is already in the past tense. It's the past tense of lose.