In a forum post the Creative Assembly has announced that Patch 1.5 for Total War: Rome 2 is now in beta while Patch 2 has been delayed "slightly" with more news coming "later this week".
Regarding Patch 1.5 the developers wrote:
"Patch 1.5 will release which contains one important fix. Patch 1.5 will enter public BETA testing today. It will not automatically update your game at this time, you can download it should you wish to participate in the BETA test by following the instructions below:
"Patch 1.5 Contains one fix: Should improve Campaign Map frame rate in the majority of cases for those people with high-end graphics cards combined with mid-range CPUs. Those people who have noted high frame rates in battle but single-figure frame rates during Campaign Map play should see a notable increase in performance."
For the changes made as part of the patch to come into effect you will need to begin a new campaign. Activating the patch involves heading to your Steam game library, right clicking on Rome 2 before selecting 'Properiters' and finally 'BETAS'.
Once there, choose "Patch 1.5".
Since release, Rome 2 has been hit by a litany of errors and bugs; the first patch for the game was released last week and the Creative Assembly has promised to continue releasing fixes until the game's issues are resolved.