Long load time for admin-ajax...domain mapping

Hi there,
I guess you are used to this one:
Problem of long load time with domain-mapping admin-ajax.php (checked with Pingdome)
http://www.losnuevosartesanos.com/wp-admin/admin-ajax.php?action=domainmap-setup-cdsso

What is it possible to do to improve that?

Please advise,
Julien