I would like to ask for every 30 min we can put

0 */30 * * * * 

or

0 30 * * * *

what if I want to make the time start at 15 min for every 30 minutes?
Eg:
12:15,12:45,13:15,13:45,14:15,14:45….

I am expecting the time trigger to execute the program start at 12:15 minutes and run every interval of 30 minutes