Potty training

Lately my daughter been telling me , me go pee or poop and brings a diaper other day she took diaper off and tried to put new one on herself but she 15 months next week i haven't even gotten toddler bed . My doctor suggested around 18 months to 24 months . I started potty training my oldest son at 12 months after i moved him to toddler bed , he used to try to get out of his crib. He got fully potty trained right at his 2nd birthday. Then my middle son he was almost 3 before got trained . What all think. ?i am undecided at the moment.