OpenCL SDK for Quartus Prime 15.1

1. The OpenCL SDK requires a separate license, at least up until v17.1. The changelog of v17.1 says "Removed requirement for Intel FPGA SDK for OpenCL license.", but I think you will still need a license for compilation and they have just removed the license check for running pre-compiled kernels.

2. The major difference between them is better quality of generated hardware in terms of performance and area utilization. There are also some new features and pragmas added in newer versions, significant improvements in area report, and many bug fixes. OpenCL support features have also improved to some extent, but it is still far from fully supporting OpenCL 2.0 (or even 1.2). I would strognly advice against using anything below v16.1.2.

3. That will very likely not work. Even minor differences in Quartus and AOC versions generally result in compilation failures. Furthermore, a newer version of AOC will require a compatible BSP that will include IP Cores that are not compatible with older versions of Quartus.

If there a specific reason why you want to stick to Quartus v15.1?