Load Panel tab: 30.99 seconds (8 seconds to page, the rest to load the live preview)
Activate Panel tab from Ext tab: 2.5 seconds
(I did an empty cache measurement because this is my typical experience as a web developer. I regularly clear my browser cache.)
There are two culprits here, one major, and one minor.
The major culprit is page weight. I'm getting 50 KB / sec download speeds (typical corporate network proxy on my end). The page is 6.87 MB total (after opening those two tabs). ext-all.js takes 14.25 seconds, sencha-touch-all-compat.js (live preview) takes 22.79 seconds.
The minor culprit is the processing time to bootstrap the live preview. It takes 2.5 seconds to switch tabs, which is almost entirely due to the live preview.
Recommendations:
Never show the live preview by default when opening a new tab.
Reduce the page weight (don't use ext-all, don't use sencha-touch-all-compat)
Hmm... cleared my cache and it took about 3 seconds to load the app. Ext api page was almost instant for me. Cleared cache and loaded Ext.Panel and it took about 5-6 seconds but wasn't that bad IMO.
I'm not surprised. You're probably sitting right next to the server (in a manner of speaking). I'm in a different continent and behind a slowish proxy. I'm not saying the problem is on your end, I'm just asking to please cater to users who aren't on a perfect network. I'm sure your chinese users will appreciate a faster docs app.
If I can offer some advice, try running the docs app through a proxy that can simulate slow networks (I use fiddler). I have users from china accessing servers in Denmark, and that's the only way I can simulate their experience.