It depends on what it is.
I can do 6 sides, which is 1 side every 10 minutes. 1 side of A4 is around 30 lines, so I write 1 line in 20 seconds on average (which isn't very quick actually, try it out).
However, factor in thinking time, reading questions, hand getting tired, etc. and you've probably decreased this by ~1/3 (but it still depends).
I think it's only a problem if you can't write more than 2 sides of A4 in an hour (if that is the case, it's not being slow at writing, it's because you spend too much time thinking). If you're doing less than 2 per hour then you won't be able to write enough for any subjects which require extended answers.