Code:
UPDATE PS_GameDefs.dbo.Mobs
SET Exp = 0
WHERE MobID = <Search 15er Mobs>
Code:
UPDATE PS_GameDefs.dbo.ExpDefs
SET Exp = <YourValue how much is needed for Lv up on 15>
WHERE Level = 15
That's the best way - i don't know where the value for Kill another Player is stored but it should be enough with the code above.
If you have an exp-boost from 100.000 there is now wonder why your char level'd up
So increase the EXP needed for lv 15 ->16