To give you an idea I have hatchlings out of the eggs taking fuzzy rats

If the animal is 1.5 years and eating fuzzy rats I can only assume that

A/ It is severely underweight and has been close to starved

B/ YOU are severely underfeeding it if the animal is within healthy weight range

C/ The age is wrong

To come back to the question is comes down to feeding, age and how much of the prey is used for growth. It can be once a week like it can be every 4 to 8 weeks or more.

Right now the important is to assess whether this animal is fed properly based on size.