It's hard to say because... Someone with medium chakra could last as long as someone with High chakra is he has better chakra control.
If kakashi is able to dramatically decrease the chakra consumption of his techniques it would make it seem like he has a massive Chakra pool. However, Naruto has natural massive chakra reserves meaning that even if he never has great chakra control he would still be able to outlast Kakashi.
However, because of recent event's i would say he has high chakra, why? Well you have to remember that not only does kakashi have a massive disadvantage because his sharingan naturally takes allot of chakra especially when you are a non Uchiha. Kakashi has not only gotten passed that effect he is also shown to be able to consistently use it, despite his so called Low Chakra and him being a Non-Uchiha.
Taking all that in to consideration i would say it's safe to say that he has High reserves. Well, then again that would depend on who you believe to have high chakra. If high chakra is people like kisame, then i would say kakashi is low-medium.