I think 20 minutes delayed data is fine. If your results are still good, you might have to spend a few months testing with real data (and you might have to make some investments for that), but it will be worth it because you know the data being delayed wasn't an issue.
If the results are bad with the delayed data, then you know that the strategy never really worked and you can move on.
If the results are bad with the delayed data, then you know that the strategy never really worked and you can move on.