The most important question is whether or not the area is played, meaning can the players actually go there or is it just “scenery�.
If the players can’t actually get to the area, then you can do a lot of improvement by replacing a lot of the 3d detail with 2d texture detail.
If the players do get to play in that area than you can still improve the performance by doing a simpler cleverer design at the cost of some small visual downgrade.
For example consider the design below.
The back and the seat portion of each chair is one continuous surface. This reduces the cost of each chair to pretty much just the cost of one divider…in the example below this is just 8 triangles.
You can add more detail to the chairs now through the texture you use for them.
If the players never actually go to this area then you can improve both performance and visuals even more by removing the back and top surfaces, since they can’t be seen from the field, and then you can even use an alpha texture to “fake� the separation of each chair from one another and get something closer to your original design.

