I found a solution.
For anyone else looking, in the moveit generated package config/joint_limits.yaml file, resides the following configurations:
joint_limits:
shoulder_pan_joint:
has_velocity_limits: true
max_velocity: 3.15
has_acceleration_limits: true
max_acceleration: 3.15
shoulder_lift_joint:
has_velocity_limits: true
max_velocity: 3.15
has_acceleration_limits: true
max_acceleration: 3.15
elbow_joint:
has_velocity_limits: true
max_velocity: 3.15
has_acceleration_limits: true
max_acceleration: 3.15
wrist_1_joint:
has_velocity_limits: true
max_velocity: 3.2
has_acceleration_limits: true
max_acceleration: 3.2
wrist_2_joint:
has_velocity_limits: true
max_velocity: 3.2
has_acceleration_limits: true
max_acceleration: 3.2
wrist_3_joint:
has_velocity_limits: true
max_velocity: 3.2
has_acceleration_limits: true
max_acceleration: 3.2
I changed all the 3.15 values to 1.00 and the 3.2 values to 1.2.
Those figures were arbitrary. Not sure it there is a way to set better values but the UR5 is slowed down.