Amazon takes 30% not 70%, but VAT applies also to sales and not to donations.
So depending on your country, 50% to 70% of the money will go Sweet Home 3D project.
The commission taken by PayPal depends on the amount you pay and your country. For $15, they should take 7.2%.

The Amazon version is up-to-date. When a new version is released, there might be just a delay of a few days before it's updated on Amazon too, the time for them to review the new version.