Extending morning sleep

My toddler sleeps through the night great but over the last few months he’s been waking up between 5-5:30 rather than his typical 6-6:30. It’s killing me! Mostly because I need that extra 30 minutes to prepare for the day. He usually is quietly playing or standing in his bed, but sometimes he cried out and I have 2 concerns. 1. We are trying to move him to his own toddler bed, I’m worried he will get up out of bed extra early. 2. We were going to move baby into his room in the next few months to share and I don’t want him waking her up early either. I’d love to have his sleep well established- just sleep till 6/6:15 before we make changes but it’s been going on for months now and I’m not sure what to do. We tried making bedtime a little later, it worked for 1 night but then didn’t seem to make a difference. For reference he goes down for sleep 7:15-7:30pm and is meant to sleep till 6:15, like he used to, but is waking at 5:30am.