First of all, you have a lot of RBS : 25 !!!
How many simultaneous connections do you have (at max) ???
Well, apart from this point, let's answer your questions :
increasing the size of a rollback segment often means turning a rbs offline, dropping it, and recreating it using a greater value for the initial extent.
In your architecture, there are 2 bad things :

1) you do not have optimal values set. this is horrible since Oracle spends a lot of time allocating and deallocating extents for your rbs, while an optimal prevents this for small transactions (since you stay under the optimal value, there is no need to increase or decrease the size of the rbs)

2) it does not appear to be very wise to use the same storage parameters for all your rbs since you have big ones and small ones.

In my opinion, you should first think about the number of rbs, then design some of these rbs as big ones (let's say 2 for example), and the others as small ones.
Big ones would specifically be used for big transactions, using : set transaction use rollback segment ...

hope this helps, and ask for anything else