Still no solution for the Sava and Stay button delay but !! Important note for those installing mod_pagespeed with Prestashop. I had to edit my .htaccess file with the following to prevent page speed from rewriting the path to thumbnails in the product back office; image not available:
<IfModule pagespeed_module>
ModPagespeed on
ModPagespeedDisableFilters inline_images,resize_images,trim_urls,rewrite_style_attributes_with_url,recompress_images,extend_cache,convert_meta_tags,
ModPagespeedEnableFilters remove_comments,collapse_whitespace,rewrite_images,outline_javascript,remove_quotes,make_google_analytics_async,combine_javascript,inline_css,resize_mobile_images,pedantic,
</IfModule>