Question

i shall remain absent from school ___ 15th next month.​

Answer 1

i shall remain absent from school till 15th next month

Answer 2

I shall remain absent from school until 15th, next month.​

• Until in the above sentence is the preposition of time. (Till can also be used instead of until, however, it is less used in formal conversations.)
• Until indicates a time period in which certain action is happening.
• In the above sentence, the activity is remaining absent from school.
• The activity does not happen after the mentioned time is over.  Here, 'I' will be present after 15th, next month.