kill @e does not kill large or medium size slimes

This effects all versions across the board on PC.

When I begin play in a creative world I like to set it to Peaceful and change gamerule to domobspawning false but the command to quickly remove all passive creatures in the entire area has a flaw.

 When I do /kill @e I have to then go to the slimes and do it 2 more times until they are finally all removed and I can begin to play.

 Can it be made that slimes die when kill @e is used whether they are large or not?