I recently noticed my 16 month old is still sleeping as much as he's ever slept. The problem is, he's been a great sleeper since he was 3 months old, easily topping 12 hours a night in most cases.
Now that he's 16 months, he's STILL sleeping from 630pm to around 8am every morning, and yes, he sleeps through the night with no waking. I camp the baby monitor to listen for him, sometimes it keeps me up at night as I worry thinking I'll miss him cry out to me, but he sleeps through the night.
His normal schedule is night 630pm (sometimes he falls asleep around 7-715. He wakes up anywhere from 730am to 8am, and then goes right back down for his morning nap from 930 to 11. He wakes up from 11 to around 1230, and desperately seems to need a nap, like he just can't stay awake. He'll sleep from around 1230-1 to around 3. Most often we have to wake him up, and that's a process itself.
How much sleep is too much? He's sleeping anywhere from 16-18 hours a day, and while I certainly don't mind the "me time" it seems like we're forcing him to stay awake and he just can't seem to handle it.