Hi,
You may break down jpeg decoding and h265 encoding. The following pipeline can check if jpeg decoding is working:
gst-launch-1.0 -vvv v4l2src device=/dev/video0 do-timestamp=true ! image/jpeg, width=3264, height=2448, framerate=15/1 ! jpegparse ! nvjpegdec ! 'video/x-raw' ! nvvidconv ! 'video/x-raw(memory:NVMM),format=I420,width=1920,height=1080' ! nvoverlaysink