You are supposed to get to the airport two hours in advance for international flights. That's more time than some people allow, but that's what the airlines call for. And check-in at the international airport often takes a lot of time, with very long lines, a lot of time for hand search of baggage and so on. Realistically you need at least 1 to 1 1/2 hours, with 1 1/2 bettr, and the 2:45 from Placencia would definitely NOT leave enough time.
--Lan Sluder