I saw Why is tikz so much slower when plotting a huge amount of data than WYSIWYG plotting tools? that pgfplots can be configured to do the plotting only once. How to do this? I have a document with many graphs and repeated runs takes so much time.
The details of this are described in
Section 32 Externalization Library of the tikz/pgf manual.
Basically adding the following to your preamble should be all that is needed: