Upgraging couchbase 4.x EE to 6.5 EE too slow

We are upgrading the couchbase server 4.4.1 to 6.5
As mentioned in the official documentation, we first upgraded it to 5.5.6 and then to 6.5.
It is picking up and upgrading indexes and documents without using any restore methods, however, it is taking a lot of time(more than a day and still not completed)
We have 5 buckets with 1 bucket having 2 million docs and rest with 100-1000 docs.
Is this the usual behavior? Is there a way to make the upgrade faster? Or should we uninstall couchbase 4 and install couchbase 6.5 and use cbrestore?