I'm 15 years old and I'm from Germany, I have a new sister for 3 months, and last time my parents have forgotten me and they are bad with me, and I want to get a serious intro to the hospital, but not to die, as my parents to value me more
Try talking to your parents. let them know how you feel. Try to interact with your new sister and show interest and this will show your parents that you are mature and caring. Don't wish yourself ill! That is not the answer. Talking to those who care for you normally works out well! 
good luck
I agree with katie2017 . The best thing to do is talk to them. A new baby requires alot care . Maybe try offering to help out with her . That will show your parents that your interested and care for your new little sister and it can also help you and your little sis form a bond. Your parents probably dont realize how your feeling . Their probably exhausted . Helping out with her even in the littlest ways really means alot . I have six children and my 3 youngest arent even a year apart. My hands were full but my older 3 helped out anyway they could and it meant the world to me and made me very proud of them too. Please dont wish to be ill . That wouldnt solve anything . Being an older sibiling is a really cool thing . You might not see it now but , you will later. Hang in there . ☺. Plz keep me updated .