Thanks Maggie for your reply, yes you are correct about having PR in the first place. What's the difference between RR 155 and 157?
155 vs 157 is generally about length of validity.
Travel validity will vary depending in your circumstances:.
If you have lived in Australia for 2 years (730 days) in the last 5 years as a permanent resident or former citizen or former permanent resident
You meet what is known as the residence requirement and might be given a 5 year travel validity on your visa.
If you have not lived in Australia for 2 years in the last 5 years as a permanent resident or former citizen or former permanent resident
You might be given a maximum of 12 months travel validity on your visa if you can demonstrate substantial ties that are of benefit to Australia.
Check the substantial ties documents you need to provide under Step by step, Gather your documents.
If you meet the requirements only because you are a member of family unit of a person who holds this visa
You can only be given a maximum of 12 months travel validity on your visa.
If you don't meet the requirement, but have compelling and compassionate reasons for departure
You might only be given 3 months travel validity on your visa.