So, every time I open Bambu Handy app, camera stream takes about 10-20 seconds to start…
When I am on mobile network it takes even longer, or it does not start at all…
On Bambu Studio it starts faster, about 5 seconds, but is is still slow to start…
How is it at you guys? Same, or better?
Note: I am 100% sure it is not due to my network 
Nop not your network I have noticeed the same thing Lan or Wan - Another thing for Bambu Lab to sort on next update.
On both bambu handy or studio the camera view is like 2 or 3 seconds. Which seems normal for me thru out the various updates.
I can remember one update version where camera views were iffy. But not since then.
i suspect the difference may be in the printer itself - it’s slow for me like the OP described using my P1P integrated camera. it’s 10x faster for you, i’m guessing you’ve got an X series printer?