Lingq iOS keeps loading very slow for me when opening up lessons, but also for basic opening and syncing the app main pages. Even when I just had a lesson open, but go back to the main page for something, then reopen the same lesson, the load time can be slow enough for my device to wanna go to sleep mode before it completes. (the sleep is setting dependent, I know, but still 
I’ve just run some tests, and the app and the website open lessons in almost exactly the same time, ~1.8 seconds to download the lesson data, and a fraction of a second after that to load (same lesson, of course).
Are you sure this couldn’t be a network problem? If you have LTE on your device, have you tried turning off wifi and testing that way? I know my ISP has problems with our MP3 server, but if I connect via VPN or LTE I can download the mp3s fine.
By the way, you might be thinking that it should be faster to open a lesson that has been downloaded recently. Lessons are cached for offline use, but we always try to fetch the latest version from the server. Displaying the cached data and then displaying the new data when it arrived actually made the interface appear more laggy when we tested it.
If you know a lesson has been downloaded to your device and is up to date, you can momentarily enable airplane mode via iOS’s control center so that the cached version gets displayed.
I did a quick test and load times do seem better this this morning. I’ll let you know if it slows down again, and if so, under what circumstances. Thanks!