evermotion trees mats have many times very high subdivisions and it makes any 64bit machine slow.
I'm amost sure your mat's subdivisions are 20 or even more, unless you are making a close up of the trees & leafs, simply set the subdivisions to 8. it would still look very nice and it would render 70% faster.
other choise is to not to use evermotion trees, nowadays there are many HQ free trees in the net, use them.
using vrayscatter or any other max scatter is perhaps the best option is your are having several or many trees, as the scatters make instances, you should not have problems with huge render times.
have you set the dynamic memory of your vray 64bit according to the amount of cores you got installed?
ufff...it could be many othe things that slow your rendering.
good luck