On your questions:
1. Why I'm not able to download the Q1 2015 version?
The 404 error appears because the account you are using had never downloaded Data Access before. At this point the error is resolved for the account and you can download Data Access Q1 2015 from here
2. Can I make .rlinq work without installing Q1 2015?
The support for .rlinq files is part of the Visual Studio integration of Data Access, and it was deprecated in Data Access Q2 2015. The latest version of Data Access that supports .rlinq files is Q1 2015. As a note, if you decide to use Data Access Q1 2015, you will have to maintain your application in Visual Studio 2010, 2012, or 2013. Data Access Q1 2015 does not support Visual Studio 2015.
3. Do I need to install Q1 2015 even if I want to migrate to Fluent Model as you mentioned above?
Indeed, Data Access Q1 2015 is a prerequisite for the workflow described here
I hope this helps.
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