So, I can't really answer your question exactly, having not been in that situation, but here is my experience:
That age has really bad separation anxiety anyway, no matter what, even without big changes. Do the teachers have strategies for managing it? I ask because I tried to put DD in a two-hour morning daycare, just on a trial basis when she was 14 mo, and she was really upset about it. Moreover, the teacher (who was not an early dev specialist, just a parent--it was kind of a co-op thing) was nice and really cheerful, but there were 12 kids, 2 adults, and the adults were used to dealing with older kids (2+)where sometimes the strategy of ignoring a tantrum was more effective. So DD did not get the one-to-one attention that she was used to, even when she was really upset.
I saw that she wasn't adjusting and pulled her, because it was sort of optional anyway for us. But I really think that if she had had a chance to develop a bond & trust with a particular caregiver, that it would have been OK, but that just wasn't the situation. What are the ratios at your daycare, and how do the teachers help him deal with the new situation? I also think DD was just overwhelmed by the sheer level of activity and number of kids. A quieter space or corner also might have helped her. Just some thoughts/things you might want to look into.
If they don't have strategies for helping a kid adjust, I would look elsewhere.
That said, it may just be a rough age for transitioning to daycare, and he will get over it eventually.
