How much and how often do you feed your 4 month old?

My baby gets fed 6oz every 3-4 hours 30oz a day. His last appointment he was 15 pounds. Our pediatrician told us to feed him double his weight. So he’s 15lbs he should get at least 30oz... well it’s been a few weeks since then and I’m wondering if I should up the amount? He’s not fussy and sleeps well at night but I can’t help but think he’s not eating enough🤦🏽‍♀️