Nursing time

My baby has breastfed and had formula from the beginning because my supply was low. She has always taken at least 20min nursing on one side , sometimes 30min. Lately she has been nursing about 10min on one side (she is 2months old). I don't know if I should supplement more since she isn't taking as long to nurse, so maybe she isn't drinking enough. Or if she's just gotten faster at nursing? Do babies get faster at 2months? I thought that happened later. Helpppp. Thanks!