You can get the entire Kanto region of badges completely out of order, so there really is not "15th" badge or gym leader.
Going in the chronological order of how you battle them in the original Red and Blue versions, Blaine would be the 15th gym leader. Blaine is not on Cinnabar Island due to a volcanic eruption, so he is in the Seafoam Islands. Take the first ladder upwards that you see when you enter the Islands to find Blaine's make-shift gym.
the 15th gym leader in soul sliver is blaine and he uses only fire type pokemon
He's in the seafoam islands.
no you have to beat the gym leader
You go to the dragons den behind the gym.
Blue is the Viridian City Gym Leader (Badge #16)
well than the gym leader comes and gives you the badge i thik
You must beat the gym leader Sabrini. She uses phsycic type pokemon.
beat her and then go to dragons den behind the gym. talk to the elder and answer some questions. once you've answered all of them the gym leader will come up and give you the badge.
If in numeral order the 14th badge is in Celodon City
she would want you to go into the dragons den and fight the old man then she will come and give you the badge................................
You get it from Professor Oak after you beat Blue ( the Viridian Gym Leader.)getting your 16th badge. Go to Pallet town and talk to him. after that you can go to Mt. Silver.
to get the gym badge from Clair you have to go to the dragons den then take the masters test when you pass she will give you the badge then storm off after this she will give you the dragon pulse TM