Strategies for apps dealing with large interdependent data sets

[Larry Martell]

I have to build an app that has many (~15) interdependent selection
fields that come from large datasets across multiple different types
of databases.

For example, field A might have 10 values in a drop down, and when the
user selects "FOO", then field B's drop down gets populated with 30
choices only applicable to "FOO". Then a selection in B of "BAR"
causes drop down C to get populated with 100 choices only applicable
to FOO/BAR. And so on.

The 2 ways I can think of to do this are:

1) each time a field is chosen send an ajax request to get the values
for the dependent fields

or

2) pull all the data when the page is initially rendered and do it all
on the browser without going back to the server

Obviously, the first will cause a lot of delay each time a field is
chosen, whereas the second will cause a big delay to first load the
page, but then it would be responsive after that.

What I am wondering is, are there any other strategies for a problem
like this? How have people here dealt with a situation like this?