That's definitely slower than normal. The longest import I've had yet has been about 24 hours from a classic board that has 1.1 million posts and about 80k users.

Memory *could* come into play if you have a number of topics with a large number of replies as when it imports them, it reads all of the replies of a topic into memory and then writes them to the new database.

The biggest factor is probably disk speed as there are a large number of database queries done on each refresh, so if your disk speed is slow it will definitely lead to a slow import.