Which SDK version I can use for NRF51822 chip ?

At this time my project is at very beginning state, I am picking up right tools to start my project development. I have spent good amount of time to research about my issue but still not sure. That's why I plan to ask this question as per my current situation.


1. PTR5518 Module from XUNTONG TECHNOLOGY (nRF51822 chip)

2. Previously developed project based on SDK 9 on same hardware.

3. Project is simply replacing a TTL communication, ble_app_uart example is used.

Question 1: Which SDK I can use for my project ?

Question 2: Which softdevice I can use for my project ?

I am looking for latest possible SDK but I am not sure I can use SDK 16 or not ?