Purge the events you do not need first, then see how much space you save and also if the performance improves.
You should also check to see if it's the Sql transaction log that is big rather than the actual database. If it's the transaction log, then truncate it - we don't use it for recovery with ePO.
You don't say which version of ePO or Sql is used, but you might also want to run some basic database maintenance too.
Perhaps use the sqlmaint utlity to rebuild the indexes and squish the dead space in the database.
See how you are after all that before thinking about moving ePO.