Galileo took six years from Earth to Jupiter.
Cassini-Huygens took three years to reach Jupiter and six years to reach Saturn.
New Horizons took one year to reach Jupiter.
Juno was launched in 2011 and is planned to arrive at Jupiter in 2016, after five years.
Why is JUICE so slow? Are agencies using a slow technology to save costs and energy, are the planets poorly alignedheh heh, or there some other boundary conditions?