The 2% figure isn't a study of the fraud rate, it's just a survey asking academics if they've committed fraud themselves. Ask them to estimate how many other academics commit fraud and they say more like 10%-15%.

So which figure is more accurate in your opinion?

See my other reply to Matthew. It's very dependent on how you define fraud, which field you look at, which country you look at, and a few other things.

Depending on what you choose for those variables it can range from a few percent up to 100%.

Those 15% is actually if they know someone who has committed academic misconduct not fraud (although there is an overlap it's not the same), and it is across all levels (I.e. from PI to PhD student). So this will very likely overestimate fraud, as we would be double counting (I.e. Multiple reporters will know the same person). Imporantly the paper also says if people reported the misconduct it had consequences in the majority of cases.

And just again for comparison >30% of elite athlete say that they know someone who doped.