How can i improve performance lag in reading project area via REST API against Plain JAVA APIs!!

Hello everyone,
I am trying to read below mentioned data of project area -
Name, Summary, Description, Process template id, process sharing status, master project area name, master repository url, Access control, Read Access List.
To read these details for roughly ~140 project areas
- Using plain JAVA API's , the time consumed is ~1 minute.
- But to read the same details using REST API's, it is taking ~7 minutes.
Approach followed in REST is
- Using "root-services" fetched project areas url,
- read all the project areas
- from each project area read, we are reading access list using "read-access-list-url"
Could you please provide me any hint,
1) why there is at all time lag in REST approach?
I know, it is because of server latency for multiple service calls(for read access list, for template id...).
Is there anything else that is a factor of it?
2) how can i improve this performance lag? (any hint, suggestion or links are helpful.)
Thanks in advance.
Regards,
Praveen S H