Could easily do it financially, the problem is you have to get the attention of someone in government that matters and prompt them to go to bat to convince numerous other people of the need to spend the money. Stray spending like that only happens as a pet cause that someone with influence champions, in doing so they burn a political marker (diverts funds from someone else's pet cause). Alternatively you have to get someone to put it into a future budget for one of the land management services, which can take years depending.
Might be far easier to get a rich person to fork over the $15m and then hand it over to the forest service, like so:
"The league plans to transfer the land to the US Forest Service in the next decade, which will make it part of the Giant Sequoia National Monument."