How much time for decision on NOIR on premium processing H1B?

[PK88]

Hello,

My H1B was approved in July 2012. 
H1B approval letter did not include a new I-94. Therefore stamping was required. However I did not get stamping since I was on OPT.

In order to get a new I-94 we applied for change of status (from F1 to H1B), but instead of change of status we received a NOIR.

My OPT expired in July and I am not in the 60 days grace period. 
We submitted our response to NOIR on July 31st. 

My question is: 
How long will it take to USCIS to review our NOIR response? When we filed H1B petition (in 2012), we did it using Premium Processing. Is there any chance of USCIS making a decision on our NOIR response within the next 15 days? 

My grace period ends on Semptember 8th. I am not sure if USCIS will give an answer by then. 

Thank you!