Your baby’s first tooth is unlikely to appear earlier than the 3rd or 4th month of life. Tooth eruption before this period is considered an early eruption. If the baby does not erupt any teeth until the age of 13 months, it is considered a delayed rash.
As your baby is 15 months old, You should wait and If your baby shows no teeth until 18 months of age, you should see a dentist immediately.
You can read complete article here : https://www.momcuddle.com/late-teething-in-baby/
if you are more concerned, you can always talk to your pediatrician too.