Apple have a set of requirements and in your situation... you cannot meet their banking and credit card requirements. At 15 you should be aware that where money is concerned those who have it and want more... protect the methods of control!
The next thing you need to deal with is that, basically the CC requirement as nothing whatever to do with a free iBooks account.
The credit card is more about making purchases from the various Apple online stores such as iBooks, iTunes (download music) apps and in app purchases and local high street stores for devices and accessories.
Apple do not have any options which do not include banking details and credit cards and care little about the problems of youth and lack of credit cards. Its a case of our club - our rules.. comply or go away!
So lets look at other options, you can distribute any eBooks created using iBA software, however you wish - providing no payments in cash or kind are recieved. You can of course take a chance and replace Samsung as Apples litigation target!
The easy way is upload an iBooks file into Dropbox and email links to fans, friends and family.
OR
Your parents could open an account and allow you to act as publisher for them! Ditto a friend with a CC.
But if your own parents would not trust you with their credit cards the above will not be suitable.
If its a book which is school or peer reralated, maybe your school have a server and would allow you to use it to allow other students to download your books.... extend that thought to approaching other schools locally or statewide....
