Does he sleep longer for you at home? If so then I would check the sleeping situation at daycare, why does he sleep so little, are they allowing adequate conditions ie, quiet room and cots? TBH, I would imagine that the added activity of a daycare would make him more tired so he would like a longer nap.
Rather than an afternoon nap I would go for an earlier bedtime, perhaps 6.30pm if youcan't get him to nap longer at daycare.