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