initial response time is too slow

Ask your hosting company, It can be a lot of things. Maybe the connection to MySQL is slow, maybe it waits for an apache process to start. It’s impossible to tell just like that. But I’m pretty sure it’s not a problem with CI’s config.

even without sql operation the issue exist and dont think its a problem with server/hosting as i tested with a html file placed outside codeigniter folder and it seems to work fine