Commerce 'Edit Order' page taking 10 seconds or more to render
Just some data for comparison - on our production server, an individual order comes up in a tad less than 2 seconds...(and on local dev it's much the same actually).  

Are you up to date with Commerce as there was some work on this I believe: https://github.com/craftcms/commerce/issues/828 (so version 2.1.5 &amp; above should be better).

Or perhaps you have some very expensive custom field stuff attached on your orders??