but , how do you approach to that?
Are you trying to hear the sound that both notes makes together or is it something else?

in ex. 13-15(maj\min 2) I could identify which is major and which is minor(and that major is always greater interval so I chose that answer).
but now I don't know what to do.

I started with the tutor "interval comparison" and right now I am working on lesson 16 without success. How to you know witch interval is greater when there is no common note? Everytime I try to compare between the two intervals , the higher notes interval sounds greater than the lower not...