Depending on how well you know your boss, it may be worth mentioning this to him first verbally and telling him your husband's problem. However, it is always a good idea to put it in writing as it will need to go onto your employment file.
Something like this should work:
Your City, State, Zip/postal Code
Your Phone Number
City, State, Zip/post Code
Dear Mr/Ms. Last Name
I would like to request a 15 day leave of absence for family reasons. If possible I would like to leave work on 17th October and return to work on 3rd November.
If approved I will be at home during this period and will be happy to assist with any problems via telephone or email.
I appreciate your consideration.
Your typed name
I hope that helps, and I wish your husband a very speedy recovery.