What do I need to develop an integration service to extract data from an Oracle DB to a SQL Server DB using Visual Studio 2015?
There are two ways to synchronize data or extract database from one (source) to another (target) database, based on what is a business requirement.
If you need to extract raw data from Oracle to SQL Server, then you can use Transactional Replication which helps you to replicate tables and its data from Oracle to SQL Server.
ETL/SSIS can be used for the same purpose, but it's for more than just replication raw data. It also helps you to extract data from the source, analyze it, manipulate it and load to target.
To configure Transaction Replication for Oracle (as source):

Both databases should be accessible on respective servers.
Oracle Client should be installed on the SQL Database Server.
Configure listener on SQL DB server. The listener It is used while we configure replication.

Rest of the steps are mentioned here.
Thanks