Follicle size question?

I just did a round of Femara CD 3-7 twice a day 2.5mg. An ultrasound today showed a follicle on the right measuring 11mm, and one on the left measuring 15mm. The tech said this was good and to start using ovulation tests. I remember her telling me a size that the egg will rupture at but I can not remember. Does anyone know what size a follicle has to be before rupture? And does this sound like good follicle sizes? Today is CD 10. Thanks!