Preemie in Nicu Question??

Ok so my sons currently 2 lbs 14 oz he’s 2.5 weeks old now his birth weight was 3 lbs 2 oz he was a 29 weeker. The Nicu recently switched him over to formula do you think that will help him put on weight faster ?? Because I was kinda iffy about them switching him to formula but they say he is taking it pretty well .