Speeding Up, Joining and Increasing Frame Rate FFMPEG
Assuming audio's not a concern,

ffmpeg -i in1.mov -i in2.mov -filter_complex
       "[0]setpts=(PTS-STARTPTS)/5[a];[1]setpts=(PTS-STARTPTS)/5[b];[a][b]concat[v]"
       -map "[v]" -r 60 -crf 18 output.mov