This all started when I needed to do a Smart RTL from a few hundred metres from the Home position. The Quad did come back but really slowly, Checked the Wiki to see if I had missed anything and but all appeared to be set correctly. Tried Smart RTL again, the Copter did come back really slowly, Then decided to just try an RTL which climbed to 30m and returned really slowly (This is the log you have seen). A bit more head scratching and though I should run the mission as this would use WPNAV_SPEED and a short mission was already loaded into the copter the only thing removed was the DO_Change Speed, When I started the mission the speed was about again about 2m/s.
The Copter has no telemetry radio and the the channel 6 trim is not set to adjust waypoint speed.
During some of the test I did try and adjust RTL_Speed but did not make any difference.
Thanks for your help