Data Deserialization time delay issue on Windows mobile 6.5

Hi,

I am developing an application on windows mobile 6.5 ,using (Visual studio 2008). I need to consume data from webservice (Rest Service json format). When i try to download 75000 of records its getting around 10mins of delay to complete the process. I tried with lot of data serialization format, some conficts with assembly version issue, some with 'Outofmemoryexception (String line  = Streamreaderobject.readtoEnd()), etc.

While is the best to solution and how can i reduce time delay to download data process. 

Framwork 3.5, C#