You can adjust the amount of ai planes in the conf.ini file (which is located in the install folder "parts\IL2DCE\").

[Core]
forceSetOnPark 0 // do not set this to 1; bomber planes don't like spawning parked in a fighter hangar
flightSize 1.0 // set a value between 0.1 and 1.0 to lower the number of planes in each flight
flightCount 0.5 // set a value 0.1 and 1.0 to lower the number of flights in each squadron
additionalAirOperations 1 // set the amount of addition air operation; set it to 0 and only the player sqaudron (and escort or opponents) is created
additionalGroundOperations 0
debug 1