If you are willing to take the RER which is easy but perhaps less comfortable than the Air France bus then 2:30 is too early. You could board an RER at 4 and you would be at the airport at 4:40. I suggest an express train, not because they are that much faster but because they stop less so there are less people moving about , getting on and off etc which makes it a more peaceful trip.

Do allow a fair amount of time to get from your hotel to the RER platform. Probably 20 minutes or so if you are dealing with luggage.

The Air France bus is more comfortable but can be victim to rush hour which can be complicated if there is an accident. Although you are going opposite traffic.