I had to verify my identity to receive my 2015 federal tax and my 2016. I went through the process but never got the check in the mail for my 2015 taxes. Suggestions?

When was all this?   Are you referring to something that happened over a year ago in regards to the 2015 return?  i.e., did you have to verify the 2015 return a year ago, or did you only recently file the 2015 return this year and then had to verify your ID?  

Do you know if the IRS ever released your 2015 refund and mailed it, and the check was lost and failed to make it to you?   Or did they never release the refund and mail it at all?   In any case, I'll tell you in the section below how to phone them.

Here's how to speak to a live agent at the IRS:

IRS:  800-829-1040  hours 7 AM - 7 PM local time Mon-Fri

Listen to each menu before making the selection.
 
First choose your language. Press 1 for English.

• Then do not choose the first choice re: "Refund", or it will send you to an automated phone line.
• Instead, press 2 for "personal income tax".
• Then press 1 for "form, tax history, or payment".  
• Then press 3 "for all other questions."
• Then press 2 "for all other questions."  It should then transfer you to an agent, but there is likely to be a long wait.

I usually use a speakerphone so I can work on something else while waiting.