Still my answer remains the same but I will try to explain with respects.
15 is stored in the class variable int and not to a locale variable of the function in that class and now you can have my first option like
1. You can have a property to whatever stored in the variable is exposed as public method.
2. Now have an Object of your Options class in the Form class where you want to create the tabs.
3. Access the property by the object.
Now I will tell you the sample run.
Say we have some static members in the class called Options.
static int i;
// Add a property for i
Now have this class access and set when OK is pressed and get this i when you need it. You can now have as many options you like to be available to all the classes globally as the properties are static