請問一個F1轉J2的問題。謝謝

請問一個F1轉J2的問題。謝謝
I want to back to China this June. I prefer to apply J2 in Beijing. How long will it take? Is it easy to get the J-2 visa?

Do I need to change it here first, then back? How long it will take to get J2 within US?

Thanks for all the infor.