My baby babbles a lot! Is this normal? She's just 4 months old and can "talk" for a ten - 15 mins at a stretch, multiple times a day.

wow you are really lucky. She must be so cute. Just let her continue with it and enjoy this moment. I guess she'll turn out to be one smart kid in future. My little one used to babble a lot too at that age, now he is 2.5 years and loves to talk in sentences and also recites poems and songs.