given the amount of private servers out there, its not impossible to realise and forsee that there will be lag the more characters there are since its a known fact that the database stores things that do not get used such as dropped items wich are not picked up, items that are deleted from ingame, account created and not used for a period of time, this is the reason weekly maintenance is done on the official silkroad servers, so they are able to "clean" the database giving it less size meaning its faster searches hence less to no lag.