Why is AirDrop so slow?
It could be interfering with existing wifi network, you can use the Airport command line tool to disconnect from other networks:

Begin by linking it to a another location:

ln -s \
  /System/Library/PrivateFrameworks/Apple80211.framework/Versions/Current/Resources/airport \
  /usr/local/bin/airport


Then, disconnect from the current network:

sudo airport -z


You should be running at about 10 Mbps !