Don’t worry too much. My baby had larger intestine previously also but all is well when giving birth. Some times it is just different babies different growing pace. If the doctor says after 15 weeks means just wait till then and dont worry so much. When my baby was diagnosed with larger intestines, it was 24 weeks and was told to follow up after 28 weeks. But i anxious! Went to seek for 2nd opinion at 26 weeks but same result. However, after 28 weeks everything looks normal. So we just have faith with our babies first.
No experience mum. But I am sharing this with you. https://www.healthline.com/health/enlarged-bladder#causes