Toget to this size was not a continuous proces for me. Between stretching to a bigger size sometimes were months or years. I have the ball sack piercings now over 20 years and only now I have 2 rings from 15mm.
I do a stretch when I feel like it or sometimes on request from a special person.
But when you stretch, make sure the piercing is healed well end strong.
I guess you can get to this size in a couple of years.