I took SP2013 team site's site collection backup before April 2015 CU updates. We applied April 2015 updates to SharePoint 2013 servers. Now, we are trying to restore site collection but it fail. Is the restoration feasible after applying CU updates?
This is a common pitfall and a good reason to look into your backup routines, especially before patching as there is no way to uninstall a patch.
Sadly, the only easy way would be if you have a test/staging farm where you have the same patch level as the site collection were at during the backup, restore it there and then move it to a separate content database, move the content database to your server where you have the April cumulative update installed, and then attach and upgrade the database.
After that you should be able to move/restore the site collection to the right site.
If you have a SQL backup of the content database, you should be able to restore the database and upgrade it. If there is multiple site collections, you probably don't wanna do this as you might loose everything that changed in the other sites since the backup.
A suggestion would be to put site collection (if possible due to the amount of site collections in your farm) in their own separate content database which would make it easier to restore a content database with a lesser patch version and attach and upgrade it if needed.