Current H1B premium processing time?? (cap exempt)

Hi. I have a question on current processing time for H1B premium application. I’m currently using my OPT, which ends on 12/31/2016. My employer filed my H1B petition (cap exempt) by regular processing a few months ago and notified me that they would need to file for a premium processing instead because there’s significant delays in USCIS this year. However, for some reason they refuse to file for premium until the first week of December. I’ve heard others complain in the past that there’s a chance for delays in premium processing as well (in which case USCIS will refund the $1225 but keep processing the case as premium). Do you have any information to the latest situation for these premium cases? If my case is filed in the first week of Dec, how big is the chance for me to get the visa in 15 calendar days (say before Christmas)? Thanks!