If lo is 15 months can she still take stage 2 milk ? Is there a need to follow stage 1 2 3 or 4 ?

Actually for me I feel no big difference between stage 2 or 3. Apart from the pricing! Taste felt the same and baby didn't even notice when I changed to stage 3. Poop as per normal too. She drinks Friso. Also I check with PD, and she said ok. Anyway, at this stage, they don't really need formula already