You're referring to the guidelines for kindy in Qld and the 15 hours requirement. It all depends on how many hours your teacher works per day. If your teacher does a 7.5 hour day, then you could just do 2 days per week, but if it's less, you may have to do a min of 3 or 5 per fortnight. Private kindys often do the 2/3 thing and run 2 groups, so one week your child will do 2 days and the next 3.
Long day care kindys are usually different.