islam nasaar

I have an offer from University A and currently waiting for University B which is my first choice. I have to accept the offer from A by 2 May. When i asked the program director in University B when should i expect a reply , he said they had many applications and the review process was postponed till 15 April. I was thinking of emailing the program director by 20 May telling him politely that they are my first choice but i don't want to wait and pass the deadline for University A and ending up no where. what do you think? Your advice is very much appreciated Thanks