rendering time

in my rails application i am search thru tables...based on a criteria....and then return the result in form of an xml document..

i have tried using Rexml::builder and also Nokigiri::builder and still i am not able to reduce the rendering time..... i.e

Completed in 1.99900 (0 reqs/sec) | Rendering: 1.39000 (69%) | DB: 0.26500 (13%) | 200 OK

how can be the time be reduced....

because when the table becomes too large say 150000 records it seems to take too much time