My Q5 blackberry requires 1.4 gb for latest version 10.3.1.1779. I freed up as much as possible (pictures apps etc) but still not sufficient.
Welcome to the community and thanks for posting. I'm sorry to hear the latest Q5 update is too big.
I've checked the BlackBerry® forums and it appears others are having the same problem. Take a look at the main community here. A more specific post has been created here.
Let me know how it goes.