Article 11 of the India - Australia DTAA specifies that interest paid by an indian company to a person in Australia can be taxed by the Indian government , once the source of interest is in India. It may be noted here that situs of the payer is the determining factor for the chargebility.
The tax rate however shall not exceed 15% of the gross amount charged. Currently the tax rate specified is 15%.
Also you would do well to check the following before deducting TDS on the remittances.
1. Does your parent company have a permanent establishment in india, you may refer article 5 of the agreement.
2. Also consider the Transfer pricing implications as this will fall under the transactions between associated enterprises.