EM console is very slow when accessing to view the composite/component details or the instance details.
We can try to improve the performance by little by following the below steps.
  1. Login to the Oracle SOA Suite 12c EM Console
  2. Right Click on SOA-INFRA and go to SOA Administration->Common properties
  3. Set the Data Display Options as shown below.
Select the option “Disable fetching of instance and fault count metrics. Each metric can still be  retrieved on demand”.


Set the Duration Details to 1 hour (based on your requirement) as shown below.



This will enable to fetch the instance and fault count metrics based on the demand also the default search criteria will display the last one hour data, this will improve the performance of the em console.
Enable fmwctl discovery cache:
Logging into Enterprise Manager Fusion Middleware Control 12c (fmwctl) takes a long time.  Sometimes as long as 45-60 seconds.  This is often viewed as slow response time, performance or hanging issues, fmwctl discovery is always performed as part of login.  
For installations with thousands of targets, fmwctl discovery may take 45-60 seconds. This delay is expected because EM discovery mbeans need to be invoked for every target.
Solution is to cache the discovery results in the servlet context and use it for subsequent logins. This discovery result will be shared by all the fmwctl users. This will still require the entire discovery to be done at least once.
Follow the metalink note 1423893.1 to enable the discovery caching.
If the caching is enabled, fmwctl will use the cached discovery results and login to the em console will be fast.The default setting is “not use the cached results”. 


All the best,
Cassio Mariani