You can select older versions after logging into the registration center. I just tried that, and I can see versions from 16.0.1 back to 8.0.035.
In the initial post you stated that you needed 12.1.5, but now you list 11 or 12. It is quite likely that you do not need an older version at all, and that the current version will serve you better in many ways.
I recommend that you build and run test cases with 16.0.1 and then, only if the results do not agree with the reference results, consider obtaining the older version. I am sure that Intel would like to be informed if the current compiler gives results that are incorrect with code that works correctly with the older compiler. At other times, the user code my have bugs that the old compiler kept hidden but the new version brings to the surface.
