I can't answer your question because I don't use pixel art. But in general, graphic packs are priced low - in all the stores. The artists hope that enough people will buy it to make it worth their while, rather than making enough money per sale to justify the work.
But I can offer you these tips:
Option 1:
- Upload your main package with the price of $15. Place that first. That makes it obvious that people must pay for the full package.
- Place your free package second and mark the block that says: This file is a demo and can be downloaded for free.
- You should be able to reorder the uploads without re-uploading the files.
Right now, the download button at the top doesn't make it clear that it's just a demo you're getting. This way it's more obvious.
Option 2:
- Split the pack into smaller packs.
- For example, place every room in its own pack for $1-$2. Place the characters in their own pack for x amount etc.
- Then offer a bundle deal as a promotion if people buy all of them.
- If someone just wants part of the pack, it's easier for them to afford.
Option 3:
- Split your demo and paid pack into two projects.
- Mention in the demo - it's a sample of the paid project and give a link.
- Mention in the paid project, there's a free demo with different license terms and give a link.
- It will solve the problem of having so much information on one page and that people might see the one license and think it applies to both packs (i.e. they won't pay because they think commercial use isn't allowed).