Firstly the good news, OnePlus has started rolling out VoLTE support for OnePlus2 in Oxygen OS 3.5.5. The OTA has reached a very few customers in India till now and that means that it is very less likely that you might have updated your device.
If not then let me tell you this, there are network issues in this OTA which will render your phone useless. You will face signal drops more than twice every minute and you won’t be able to place any calls or use data. If you are using Jio then you are going to face this problem for sure. I updated my phone last night by downloading the ROM from their website and started facing the problems. So please wait till OnePlus releases a fix.