slow rendering with backend_macosx on El Capitan

With a fresh installation of mpl 1.5.1 from Anaconda on a new Macbook Air with El Capitan, there are long delays (several seconds) when rendering a multi-subplot figure based on cut/paste a section of script into an ipython window. This does not occur with the qt4agg backend.
I think we need to ensure the macosx backend is not selected by default, at least in the next mpl release on Anaconda.