I also have this problem. I have so far used Dante on 3 webpages, which is on 3 different FTP-servers (2 different hosts). Both the back-end and front-end is really slow.
Takes about 5 seconds for the page to reload after clicking for example ‘update’ on a page, and then 5 seconds for the front-end page to reload after that. It’s really a pain to work with.
My internet-connection both at home and at work is good 25/15mbit. I do not have any issues with other themes than Dante.
I’m sad that it is like this, because I really enjoy Dante and wish to use this for more clients.