My girl is 2.4 months. On last dr visit her head circumference was 14.5 (4week visit). Now it's just 15 inch (10 week visit) just 49% increase.

A bit slower. Normal head growth is about 0.5 inch per month at her age and therefore, expected head circumference (HC) would be 15.25 inches. Watchful waiting is all needed at this time. Persistent slow head growth associated with delayed development will be of more concern.