Good morning. Under the law one of the requirements for U.S. citizenship
is that you show "good moral character." To the USCIS this means that you have behaved well, including paying your taxes. The N-400
specifically asks about whether you have paid the taxes that you owe.
Since you did not file, it doesn't mean that you are forever barred from U.S. citizenship. What you must do is file the tax return for 2014 and including a payment for the basic amount and any applicable penalties, or if you can't afford the back taxes you should enter into an installment agreement with the IRS.
In order to get approved for naturalization you need to show that you filed and you have entered into a payment plan.
It would be in your best interest to hire an immigration
attorney, who would draft a legal persuasive letter to submit with your IRS documentation explaining why your failure to pay taxes does not indicate a lack of good moral character. In cases like this it also helps to submit and present other evidence of your good moral character, for like letters and documents showing your community involvement, dedication to family, participation in religious worship activities, and so forth.
I hope this helps with your question.