I have never used POR15 but have read you must follow the instruction to the penny. I have read stories of it pealing off when directions where not followed. I have also seen the results when done correctly and it looks great. One word of caution is POR stands for Paint Over Rust. It is meant to paint over rust. Not sure how it works on sandblasted surfaces. POR15 has a special wash solution and acid etch solution to use before applying the top coat.
If it was me on a sandblasted frame I would epoxy prime and top coat with black Rustoleum. If you just want to knock the rust and dirt off with a wire wheel then POR15. If you are worried about some small rust specks left after sandblasting then you can use an acid solution like OSPHO. Just make sure the epoxy primer is okay with acid prep. Some epoxy primers are fine with acid some are not. I have used Omni epoxy primer over OSHO with no issues.