If the Data Hub size is huge, how can I optimize it?
As it is taking a lot of time to get data imported into Modules.
I would check out the article by @rob_marshall HERE . This includes the best practices and suggests ways to help optimize it as well.
I would start with the Worked Example Section and the Loading Data vs. Using Formulas in SYS modules section. That should help to cut down on the speed of the loads, and also use the dimensionality power of Anaplan to your Favor.