Will H1B upgraded to premium and then got RFE will receive RFE response in 15 days?

If petition was filed as regular and later was upgraded to premium and then got RFE.

Then, what is time (days) for USCIS to make a decision after RFE response with requested information?

Is it up to 60 days or within 15 days?

Is it required to pay $1225 again for expediting?

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.