SQL & PL/SQL

Does using "Order by " clause in each of the child clauses of the union all query reduce the performance of the query?

Because, in my java application i need to connect to no. of db servers and collect data. so using db links i connect to all of them and make one union all query.

the performance of the union all query doesn't seem to change when there are order by clauses. but otherwise, the speed is double without order by clauses.