Import content to Lithium from different Community

Yes,

However, you're not able to do this yourself but with the assistance of professional services, they can do this. As part of the engagement with PS you'll have a mapping exercise where every field or row will be mapped from your data export to the fields in the data import. 

They have done this many times over and will have no doubt done a migration from your system before so may be worth speaking with your account team or raising a ticket with support who can point you in right direction.

Thanks