There is no official speed meter or recorded maximum speed in Wii Sports Bowling. The game caps ball velocity for balance and fun. However, you can maximize your speed with technique:
In Wii Sports, accuracy and spin control beat raw speed. A 16 mph ball in the pocket beats a 22 mph gutter ball every time. Focus on consistent form, targeting the 1-3 pocket (righty) or 1-2 (lefty), and adjusting for lane oil patterns in Pro mode.
For speed runs or bragging rights, practice the "power throw" in Training mode's "Power Throws" challenge—it gives feedback on ball speed.