H1B premium upgrade is applicable for RFE too
Once the H1B application is upgraded for premium processing, all other corresponding RFEs are considered premium too.
In this case RFE response time will be 15 days.
In normal (non-premium) RFE case , RFE response time is 60 days.
Please note that these time frames are for general guidance, we have seen USCIS take more than 60 days too, based on their work load. But, this is not common.