Weight of Sofrider
According to the Sofrider page:
"Weight 14.6kg, 32.12 lbs weighed with pedals" & "Bell, Kickstand, wheel reflectors, front and rear reflectors"
Get more speed by getting lighter wheels, tires, tubes and cranks, an 11 tooth cog (if not already), even bigger rings, lower seatback, a fairing, and last but not least, a faster cadence. Do you have a big dog? Try leashing him to handlebars.
How much does the conversion kit weigh? I read 6kg somewhere here (over 13 lbs.) so if you add that to an average 30lb. mountain bike then your setup is very close to average.
Cheers, Brian