Backflow vs low flow hose?

Our plumber added a new hose faucet for us and it has a backflow prevention device on it which is fine, but we seem to have to turn the water on high to keep the water from flowing out of the device... if I want to have a hose just watering slowly is there a way to fix this?
Thanks -

Call the plumber back. He can replace the part that is leaking and stop the problem.

hose

It is defective if new, and worn out if it is the old one.

Thanks to both. I was afraid it was maybe just "supposed to" be that way, in the way that lots of newer things seem to be disappointing in some way. This is a relief, I'll call the plumber.