I had similar problems with a large 2GB PST file with loads of folders.
First of all, the messages may fail to import if they are larger than 10MB. Have a look at
this page - you will need to modify the server and the registry of the machine you run the PST Import Wizard on.
If that fails, then what I would recommend is this - create a new PST file for each folder in the original PST file, so you end up with multiple PST files - one for each user-created folder.
Open the large PST in Outlook. Create a
new, empty PST (could be something like File > New > Personal Storage Folder). Drag a folder from the original PST file into the new one. And then make another new PST, drag the next folder into it and so on. It might be advisable to do this on a new user profile or computer so as not to interfere with anything.
After this, just import each small PST file one at a time. You may need to run
Scanpst on the original; as even though just the Inbox folder remained on mine, the size still remained 2GB.
I'm not saying that will work; but it did for me. I had a total of 6 PSTs to migrate and only one needed this much work to get it to import successfully.