Milk quantity

Hello moms, my son is 15 mnths old and had stopped taking milk during day time I give him milk with some shakes. I usually put 2 spoons of formula in his shakes he drinks twice a day. But at night he drinks around 300 ml milk while sleeping. He only drinks from bottle while sleeping. But I want to stop that and I am worried that if I stop his night bottle he will not get enough milk. What should I do?