You have to move snorlax and go through diglet tunnel to the east of vermillion. It will take you just south of Pewter City, where gym 14/Brock is.
in the cities
you need to beat all the gym leaders johto and kanto
the sexth gym leader jasmine is in the lighthouse
cianwood city.
you have to get all 16 gym badges
in seafoam islands in kanto or mahogany in johto
get all 8 gym badges.
the 15th gym leader in soul sliver is blaine and he uses only fire type pokemon
Clair in the Blackthorn City gym uses Dragon-types. Blackthorn City is accessible after beating Pryce at the Mahogany Gym.
you dont make poffins in soul sliver
The 14th gym leader is the 14th gym you challenge, and there really isn't an order. However, in chronological order, the 14th gym is the gym in Saffron City, with Sabrina as the gym leader.
There Isn't