If you we the designated beneficiary, you actually inherited the IRA at the moment of the deceased owner's death. Because the deceased had not completed the 2014 RMD, it became your responsibility to do so in 2014. Since you did not do so until 2015, there was an excess accumulation in the account for 2014 that needed to be reported on your 2014 tax return.
Since you have now completed the 2014 RMD, you should amend your 2014 tax return to include Form 5329 requesting a waiver of the excess accumulation penalty for reasonable cause. Given that it can be difficult to get TurboTax to create the necessary 2014 Form 1099-R under these circumstances, it will be easiest to do it manually. You can get the 2014 Form 5329 and instructions here:
https://www.irs.gov/pub/irs-prior/f5329--2014.pdf
https://www.irs.gov/pub/irs-prior/i5329--2014.pdf
The instructions for requesting the waiver are at the end of page 7 of the instructions. The IRS invariably grants the waiver under these circumstances and you'll hear nothing more about it, no additional tax or penalty due with the amendment.
A single code 4 2015 Form 1099-R for the combined distributions to you of the deceased's 2014 RMD and your 2015 RMD is correct. Report the entire amount on your 2015 tax return by entering the Form 1099-R exactly as received and indicating that you satisfied the RMD for 2015. You'll continue to receive code 4 Forms 1099-R each year for the RMD distributions from this IRA until this IRA is completely drained.
