Yes, it is. Her sleep will gradually mature where she begins to go through the different sleep stages that form the sleep cycle (approximately 120mins per cycle). This will take place when she is around 4 months old. During this period, you can consider starting sleep training and to establish bedtime routine to help baby sleep better.
It's very normal ! Newborns need to sleep atleast 18 hours a day. It's good she takes long peaceful naps.