Let's assume you pay the highest income tax rate (about 40%). 40% of $15 is a whooping $6!
If all you did was to not be aware of reporting $15 in interest, my practical answer would be to forget about amending any tax return. I doubt that the IRS wants to incur the expenses to review your amended return for another $6 in taxes.
In future years, you should remember to report all your incomes. US citizens and legal permanent residents are required to pay US income taxes on their world-wide incomes unless there is a specific exemption for a particular type of income.
There is an additional issue that you should also be aware of in filing your returns with a foreign bank account. Under US law, you have a duty to report your foreign accounts under the FBAR. Failure to do so can lead to massive penalties. I would suggest checking with your accountant about submitting your FBARs. It does not necessarily require an amendment of your 1040, but if you are required to file the FBAR, it may be advisable to also file an amended return for the year.
This information is provided as a service generally and is not intended to answer any specific questions from any specific individual. No attorney client relationship is created by answering these forum questions and all readers are encouraged to seek out a competent attorney to speak with that is licensed to practice in your respective state.
You should definitely amend all returns that you can. Make sure that if you file a Schedule B that the questions regarding foreign bank accounts and foreign trusts are answered. You must also do FBAR -Foreign Bank Account Reporting if you have over certain amounts in foreign accounts.
I am an Attorney-at-Law, licensed to practice law only in the state of Indiana. Unless we have both signed a formal retainer agreement, you are not my client, and my discussion of issues does not constitute legal advice. Opinions expressed herein are those of the author, and do not necessarily represent the opinions of those who hold other opinions.