Yeah, 2.5 hours to clear customs and switch terminals without checked bags should be fine as long as there aren't major delays on the Air Jamaica flight. And like someone else said above, as long as both segments were booked as part of the same ticket, even if you were to misconnect, Delta will accommodate you on the next available flight to CMH.

If you couldn't handle going carry-on only, btw, I would recommend taking the checked bags with you to T3 and giving them to DL there even if the option exists to re-check them right after clearing customs at T4, because it reduces the chance that your bags might get lost or delayed in the inter-terminal shuffle.