Hello Caroline,
Go through following 3 troubleshooting steps 1 by 1.
Firstly, please change theme using following Steps:
1.Click on Appearance ? Themes>> Activate other theme than Twenty Fifteen.
2.Again,Click on Appearance ? Themes>> Hover the Mouse over Active theme>> Click the “Theme Details” button.
3.Click Next Arrow button on the top left side of theme until you find Twenty Fifteen. Click Delete button
4.Go to Appearance ? Themes>> Add New >>Upload Twenty Fifteen theme. Activate the theme.
Now, check various options of theme again to see if your issue is resolved by doing so.
If the problem still continues, here is another troubleshooting step:
To rule out a plugin conflict, you could try temporarily deactivating all your plugins. Does the problem persist? If the problem is gone, reactivate your plugins one-by-one, look at the site in between each reactivation, to find the conflict plugin.
And the final trouble shooting steps would be deactivating the child theme you make, and check if there is still space under footer. If there is not any problem try to find where space is coming from.If you can’t figure it out you can put the code of custom post type for products here.
Thank you!!