Rental income - commercial 15 lacs, residential 7 lacs. gst required??

Yes, since your aggregate turnover exceeds 20 lakhs.

However you may be eligible for composition scheme for service providers.

But registraton is mandatory for you under any case.

Refer- section 22 of CGST act.

The residential rental income is Exempted in term of Notification 12/2017 CT & As per section 22 of CGST Act whose Aggregate Turnover is more then 20 lac is liable take Registration in GST and if we read the definition of Aggregate Turnover in Section 2(6) of CGST Act it includes Taxable + Exempted supply . Hence you are liable to get yourself registered in GST.

Agree with Pankaj Sir's view...

Rental Income from Commercial Property : TAXABLE under GST.

Rental Income from Residential Property : EXEMPTED by Notification No. 12/2017 - CT( RATE ) , dated 28.06.2017.

Aggregate Turnover as defined u/s 2(6) of the CGST Act 2017 also includes EXEMPT SUPPLY.

Hence take GST Registration.

Warm Regards

Thank you for your reply sir. Though now this leads to the question that whether I would have to pay 18% GST on the Commercial Rent I receive? Even though my commercial rent is only 15 Lacs and Total Rent (Commercial + Residential Rent) = 22 Lacs? 

Yes only 18% on 15 lakhs

7 lakh income is exempt

18% GST to be paid on Rental Income from Commercial Property.