The following suggestions about settings in your initialization parameter file may help improve performance of an import operation.
Set LOG_CHECKPOINT_INTERVAL to a number that is larger than the size of the redo log files. This number is in operating system blocks (512 on most UNIX systems). This reduces checkpoints to a minimum (at log switching time).
Increase the value of SORT_AREA_SIZE. The amount you increase it depends on other activity taking place on the system and on the amount of free memory available. (If the system begins swapping and paging, then the value is probably set too high.)
Increase the value for DB_BLOCK_BUFFERS and SHARED_POOL_SIZE.