The BUFFERS 0 , probably is a misinterpretation of SAP.
The BUFFERS keyword is a old config parameter on Informix
This configuration have only 1.6GB of buffers to keep your data on memory (data saved on 2K pages). Depending of the database size and how much access your have, this is to low .
First , check if all your data are working in dbspaces with 2K pagesizes (onstat -d).
Then, if you confirm this, check the possibility to grow up the BUFFERPOOLS buffers.
If you have data working with pagesizes different of 2K , review your BUFFERPOOLS for this pagesizes.
To make sure the reason of the slowness of your SQL , execute it with SET EXPLAIN ON , and analyze the access (if use index, if create temporary tables, etc).