This list is probably far too short. Feel free to suggest additional questions (preferably with answers!)
Octave is probably spending this time recursively searching directories
for function files. Check the value of your LOADPATH. For those
elements that end in // do any name a very large directory tree?
Does it contain directories that have a mixture of files and
directories? In order for the recursive directory searching code to
work efficiently directories that are to be searched recursively should
have either function files only or subdirectories only, but not a
mixture of both. Check to make sure that Octave's standard set of
function files is installed this way.