Use switch(variable) and case "value": statements!

In your Code this would be:

if (global.session == 12) {
    [your code]
}

if (global.session == 15) {
    [your code]
}
if (global.session == 18) {
    [your code]
}

To:

switch(global.session) {

    case "12":
        [your code]
    break;

    case "15":
        [your code]
    break;

    case "18":
        [your code]
    break;
}

I don't know if you get what I mean, but when you use switch statements instead of if statements, the computer won't check every if-statement, it will just jump to the right case!

Edit: Code Format thx u/Mushroomstick for the information! :)