Hi,
If "Reset Palettes" doesn't work for you, you may also try to Reset Application options, but be aware - that will reset all settings to their default values.

Before trying resetting Application options I'd suggest you to check icon sizes in AutoCAD options - if you changed them (increased their size), try at first set the default size, than reset palettes again.

Another way to try is to trash "Profile.aws" file, which is in
"/Users/YOUR_USER_NAME/Library/Application Support/Autodesk/roaming/AutoCAD LT 2015 Standalone/R20.0/enu/Support/"
folder. YOUR_USER_NAME is your short user name on Mac.You need to QUIT AutoCAD before trashing this file.

Maxim