I'm just worried this is not enough sleep for him
"...for him"
How much sleep my 2 year old has (loads) or how much sleep another child who dropped daytime napping at 18 months is irrelevant to your child.
Getting enough sleep is important. There's recent suggestions by the NHS that sleep deprivation might be in a par with obesity in terms of the effect on childhood health. However there will be natural differences in what is "enough sleep" for each person.
Getting enough sleep can be judged mostly by the way a child looks or behaves -
clinginess, poor behaviour, concentration levels, tetchiness, tantrums, crying etc
There will be a transition period (up to a couple of months) to establish any changes in sleep routine. But in my experience the child usually makes up for lost sleep initially, (for example seeing 1-2h being added into the night sleep when daytime nap is dropped), then reduces overall sleep after transitioning. So it isn't a necessity of changing sleep routine to have a period of time being more tired than usual.
How much sleep does your 2 year old get?
Mine was born Sept 2014, so similar age. She sleeps usually 12 hours at night but the variation would be downwards, so 11-12h
Then she sleeps 3h at lunchtime, 12-3pm. I wake her (for the school run), she would sleep longer.
I have just, literally since the weekend, noted the beginnings of her not going straight to sleep when she goes to bed at 7.30-8pm. I could hear her awake on the monitor until 8.30pm tonight and yesterday was the same. She's normally asleep straight away, within 5 minutes.
I am just starting to think about maybe moving the start of naptime to 12.30 or 1pm, so 2h-2.5h nap instead of 3h. I'll see how it goes for the next week or two before I decide.