I'm not sure what you're referring to when you say "withheld this information for 15 years".
How PFOA should be regulated has been a back-and-forth issue at the government level since its toxicity was first exposed. Dupont is the one who completely hid its toxicity for 40 years. Once that cat was out of the bag there was nothing the government could do to hide that. The question has been what levels are to be considered too dangerous and how the government will regulate those things. I wasn't aware of facts pertaining to that role that have been hidden for that entire time period, although some reports were slow-paced and the Trump Administration apparently very recently tried to keep some new findings from going public.
You seem to be equating Dupont's sins and the EPA's sins in this regard. There's no comparison. Dupont is the murderer, the EPA is the shytty-ass DA who hasn't been prosecuting appropriately. One deserves the electric chair and the other deserves to lose their job, but don't try to equate those two things.