evolve dynamic css slowing the site?

i make a test on pingdom and the result is good, but the

http://fliper.eng.br/wp-admin/admin-ajax.php?action=evolve_dynamic_css&ver=4.1.1

use much seconds waiting… what i can make for fix it?

fliper.eng.br is my site, and have just this insue for fix, what i need make for fix tand make ajax-admin.php?action=evolve_dynamic_css&ver=4.1.1 more fast?
thanks