Earlier this week Creative Assembly reassured Total War: Rome 2 players of an update that will fix hardware issues that a small percentage of people reported. Today's release of Patch 1 for Total War: Rome 2 will fix issues to improve performance and any in-game bugs.
The patch will include a number of adjustments like frame rate fixes and fixes for any issues when running games with Direct X 10. The patch also introduces a number of fixes or specific in-game behaviours like the slow turning speed of transport ships and pathfinding of units in a Barbarian village.
For the full patch notes, Creative Assembly posted the fixes and changes on the Total War: Rome 2 wiki page.
Next week Creative Assembly will release another patch which will "include fixes for low-poly models viewed close-up, performance settings on certain hardware combinations and siege battle path-finding amongst other improvements."
If this update doesn't seem to fix your specific hardware or performance issue, the Total War: Rome 2 support forum may help resolve your specific problem.