It's a full-size pickup that seats five or six, and has enough interior space that even the long-legged can stretch out in the back seat for 1,500-mile road trips. Flat floor is cargo-friendly when the back seat's folded up.
The follicle is a functional anatomical structure which forms part of the ovary and the egg is the cell that will mature in a microscopic part of inner wall of a follicle over spontaneous or stimulated ovarian cycle in normal conditions.
A mature follicle is a follicle ready for ovulation, meaning, the egg inside it is developed and ready to be released (with the hopes of fertilization taking place). A follicle will typically release (ovulate) when it reaches maturity size. Maturity is considered 18-24mm on non-medicated cycles and 15mm+ for medicated cycles. What your doctor was saying was that as best she could tell, you have one--possibly two--follies that are quickly reaching maturity... 15mm.