Yes, you can create reports for SSRS 2008 R2 with VS 2015. You will need to download and install SQL Server Data Tools (SSDT) ββfrom the following link.
https://msdn.microsoft.com/en-us/library/mt204009.aspx
To create reports, create a new project using the report server project template found in the Templates / Business Intelligence section of the New Project dialog box. (After installing SSDT)
This is a replacement for BIDS, so much of what you see should look familiar. Not sure about Crystal Reports datasets, but you should be able to reuse any SQL or stored procedures that may be part of them.
Should you upgrade? At some point, of course, but it is not required. SQL Server 2016 is about to be here, and you are working with a product that is more than 4 years old, and most likely will soon come out of support if it has not already been.
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