What time does he usually go to bed? And as
Often babies who have their main nap in the morning, go to sleep very heavily when they eventually go to sleep at night- as its been such a long time since the nap, and then susequently wake up early as they have slept soo deeply in the early sleep hours their body clock thinks it's 'Done' for the night.
If you are doing CC, this needs to be done at day time naps too- and so YES, if after 15 mins, he wakes, try to get him back off again by going in, for an initial reassurance, then leave and continue CC until he is aleep.
As Bobby suggested,he should really have 2 naps, to avoid getting over tired, and although SOME babies sleep well with early morning naps, in general most babies who struggle with sleep, don't sleep as long at this time, as it's too close to when they woke up from night.
Also CC will only really work if he falls asleep without a sleep asscociation ( ie you) Because when he rouses into a light sleep and you aren't there, he will wake fully and need you there to get him back off, and now he is able to fight his sleep, he would rather have a play, than go to sleep. So for babies who wake after being asleep for reasons other than hunger, are usually in need of thier sleep association ( mummy, rocking, dummy, boob, bottle etc)
TRY~
7 am wake
8am breakfast
9am Short nap ( no more than hour, but 15 mins ok, in pushchair, out and about, whever you are )
12pm lunch
1-3pm nap ( in his cot, if possible, so that he is used to falling alseep there. if wakes up before 1 hour, proceed with CC, but WAKE regardless of nap length at 3pm)
5pm
dinner
7pm bed.
Some babies really NEED a solid structure for their body clocks to kick into something more reasonable, and so until he has changed his night wakings, stick to a set routine, so his body clock is adjusted, then you can relax it a bit more when he starts to sleep through.
I imagine he will behave totally differenty for his child-carer. If they want him to nap at a time convenient to them, they will soon get him into a routine- i have looked after countless babies who "don't nap, wont eat ,don't like baths etc" who hardly protest when they are with me, and slot into my routines very easily.