I think you're right, but I'd say more like 25. This might help:
To change the keyboard size on a zumo 450, 500, or 550 device:
- Touch Settings
- Touch Keyboard
- Select the desired keyboard setting
- The three options are Standard, Large Buttons, and Auto
- Touch OK to save the change
Repeat these steps as desired.
To change the keyboard size on a zumo 220, 660, or 665 device:
- Touch Tools
- Touch Settings
- Touch System
- Touch the button under Keyboard Layout
- Touch the desired keyboard setting
- The zumo 660 and 665 offer ABCDE, QWERTY, and Large Mode
- The zumo 220 offers Standard Mode and Large Mode
- Touch OK to save the change
Repeat these steps as desired.
To change the keyboard size on a zumo 350, 390, 395, 590, or 595 device:
- Touch Settings
- Touch Language & Keyboard
- Touch Keyboard Layout or Keyboard Language
- Touch the desired keyboard setting
- zumo 350 and 390 options are QWERTY, ABCDE, and Large Buttons
- zumo 395, 590, and 5951 options are QWERTY and Large Buttons in the preferred language
- Touch Save
Repeat these steps as desired.
Note that the zumo 350, 390, and 590 also have a mode-adaptive keyboard. For more information on what the mode-adaptive keyboard is and how to use it, see related content.
I also found this info, (may or may not apply to your device):
Under the setup menu there is an option for advanced settings under advanced settings there should be an option for text size, this will adjust the size of the text on all map items.