Limit size for index tablespaces

Hello,

We have a lot of performance issues with queries selecting from tables whose indexes blong to the tablespaces BTABI

This tablespaces is the second biggest one in our system

1-is there any relation between size and performance?

2- Does the size of the index tablespace impact the bufferisation process?

3- is there any maximum for the size of index tablespace above which bufferization won't work

Thanks for your help

Meher