Professional fees below 20 lakh but charging st already

I am an individual registered for Service Tax in Bangalore but providing management consultancy services to an organization in Rajasthan. My yearly billing is about 18 lakhs.

Previously, I was charging 15% Service Tax.

However, I read now that annual turnover less than 20 lakhs are exempt from GST. 

Should I stop charging my client for GST or should I start charging 18% GST? Do I have to do any registration in Rajasthan? If yes, how?