The tools are set to 15mm as a default once the images are scanned into the software. You can check the depth by pressing the "I" key on your keyboard; for information. Tools default depths will be purple in color as shown below. See the article on setting depths to learn more about editing depths: https://osaapamerica.zendesk.com/hc/en-us/articles/115007688027-Step-6-Setting-Depths-for-Cut-outs
If you attempt to save the file before changing the depths;you will get the message "Tool with Default Depths Detected".
You can still save the file over the message.
The purpose of the message is to remind the user to chaneg the depths.
NOTE: Forgetting to change the depths from the default depth, is the most common mistake users make.