I assume you mean a dependant student visa, rather than a partner visa.

A partner visa is for the foreign partner of an Australian Citizen or Permanent Resident.

The time for a dependant student visa grant, after receiving confirmation of enrolment from the university, can vary depending on the complexity of the applicants history.

Normal processing times can vary depending on the location of the applicant, and on the numbers of applicants at any specific time.

A current notice on one Embassy website is:

Processing times for Student subsequent entrant visa applications processed by New Delhi are currently longer than the published global visa processing timeframes across all sectors. We have received a high number of applications for subsequent entrant applicants and are seeking to process them as quickly as possible.

I saw one being granted 15 months after application.

Some applications take longer for various reasons.

Important Information for Student Subsequent Entrant Visa Applicants.

The Department of Home Affairs (Home Affairs) prioritises complete applications where the applicant has also cleared Australia’s health requirements.