You can choose the option normally fifteen. If you want to change this number, you read this post.
Go to "common" folder in “C:\Program Files\Paradox Interactive\Hearts of Iron III\”.
Open the “defines.lua” file with Notepad program.
“NUMBER_OF_VICTORY_CONDITIONS” : It allows you to specify the total number of selected conditions. If you want to select 20 options. you change “NUMBER_OF_VICTORY_CONDITIONS = 20”.
“VICTORY_CONDITIONS_TO_WIN” : The number of targets needed to win the game. This number should not be more than “NUMBER_OF_VICTORY_CONDITIONS"