The following suggestions about usage of import options may help improve performance. Be sure to also read the individual descriptions of all the available options in "Import Parameters".
Set COMMIT=N. This causes Import to commit after each object (table), not after each buffer. This is why one large rollback segment is needed. (Because rollback segments will be deprecated in future releases, Oracle recommends that you use automatic undo management instead.)
Specify a large value for BUFFER or RECORDLENGTH, depending on system activity, database size, and so on. A larger size reduces the number of times that the export file has to be accessed for data. Several megabytes is usually enough. Be sure to check your system for excessive paging and swapping activity, which can indicate that the buffer size is too large.
Consider setting INDEXES=N because indexes can be created at some point after the import, when time is not a factor. If you choose to do this, then you need to use the INDEXFILE parameter to extract the DLL for the index creation or to rerun the import with INDEXES=Y and ROWS=N.