>>1 what you describe as an unattachement to this world, can probably be describe as a lack of purpose. A "purpose" is basically anything that makes life on earth worth living in. It can be a relationship to another human being, or even a pet. It can also be an activity that you enjoy, or an action that you like to perform that gives you fulfillment, like bringing smiles to other people's faces. It can also be the future itself, a dream, a goal, an unsolved puzzle, or an unanswered question. It can even be finding yourself.
Some people can discover their purpose at an early age and build upon it as they grow older, for others, finding it may take more time, you're fifteen and not knowing what you want out of life at that age is fairly common.
My advice to you is to try new (safety first) things, meet new people, do nice things, research things that interest you, etc. You can even just do nothing new and eventually something may cross your path.
This is just my interpretation but I hope that it helps you. Good luck! :3