If she will drink bigger bottles less often that is fine! Providing she is getting what she needs, has plenty of wet and dirty nappies and is alert in her A times she will do fine. Formula fed babies do go longer between feeds than breastfed babies because formula takes longer to digest.
If she is sleeping through on the millk she gets in the day then she is getting enough, she will wake hungry in the night if she needs more. There is a big growth spurt around 16 weeks so you may find you get night wakings for food for a few days. If she wakes at night and can't be resettled easily I would assume hunger as she is still young for sleeping through. Keep an eye on her weight gain too as that will tell you if she is getting what she needs!
Laura