Skylake's IMC officially supports only DDR3L with a voltage of 1.35, and it officially supports DDR4 at 1.2 V. This might seem a little counter-intuitive to some users, as the entire reason for continuing DDR3 support is to make it cheaper and easier for customers to upgrade to the new Skylake platform, but these voltages are likely used to avoid damaging the IMC. Although it would be nice to use any DDR3 from 1.35 V - 1.65 V, running at these higher voltages could burn out the IMC and kill the processor over time.
If this is the case, though, then why do OEMs such as Gigabyte support DDR3 at 1.5 V on some of their motherboards? And why do others such as Asus and ASRock support DDR3 at 1.65 V? RAM running at these voltages might be capable of operating on the motherboard without causing damage to the board itself, but again, over time it will likely damage the CPU. So if you don't have DDR3L on hand, you are probably better off to go ahead and spring for the more expensive DDR4.