Skylake's hardware encoding would be different from ffmpeg's medium preset (which I think uses x265 as actual encoder). Hardware encoding is generally real-time, but the quality is usually not on-par with x265 or other good software encoders. I don't know whether Skylake support p60 encoding in hardware.
I'm not sure the NUC6I5 is capabale of real-time x265 encoding in software.
The specifications of the i5-6260U with Intel® Iris™ Graphics 540 are the following.
Hardware Accelerated Video Decode
Gen 9 LP implements high-performance and low-power HW acceleration for video decoding operations for multiple video codecs.
The HW decode is exposed by the graphics driver using the following APIs:
• Direct3D* 9 Video API (DXVA2)
• Direct3D11 Video API Datasheet, Volume 1 of 2 33 Interfaces
• Intel Media SDK
• MFT (Media Foundation Transform) filters. Gen 9 LP supports full HW accelerated video decoding for AVC/VC1/MPEG2/HEVC/VP8/ JPEG.
Note: HEVC – 8 bit support.