H1B transfer filed on Apr 14'2015, no receipt yet

My future employer sent my H1B transfer documents to USCIS (VT center) on Apr 14 and they received those next day. Its almost been 3 weeks, since I am waiting to receive the case number from USCIS…i am not comfortable in resigning from my current employer until I receive case number…its a regular processing…any idea, when will I receive it? Is it delayed due to heavy load on USCIS due to H1B lottery going on ?please help