Does the Samsung Galaxy S6 record video using H.265?
GSM Arena have posted a review of the Galaxy S6 which includes a downloadable 2160p video clip. Running it through mplayer reports the following:

Opening video decoder: [ffmpeg] FFmpeg's libavcodec codec family
libavcodec version 54.35.0 (external)
Selected video codec: [ffh264] vfm: ffmpeg (FFmpeg H.264)


I take this to mean the device records in h264 only.