That's what the triggered event I talked about was for..
You should have a triggered condition with the system compare condition..
so only call the function every x seconds
or when all enemies of the first wave are destroyed
adding a system trigger once condition could help also if you are changing the wavenumber in a different (triggered) event, so the enemy-wave is only called if the wave number changes..
Thre are so many ways to prevent this every tick issue, that only you can decide what is the way for your game..