Feeding questions

My baby is 15 weeks old and exclusively formula fed. He used to eat 5oz every 3 hrs but we increased it to 6 oz thinking he would last at least every 4 hours. Well, he could barely get to 4hrs--he will only last up to 3.5 hrs even with the 6 oz.

He last feeds at 9pm then wakes up at 7am. No feeding during the night, for the most part.

Is 6oz every 3 hrs too much?? Or is he just catching up since he sleeps a long stretch??