Yes, using skins in Spine can improve runtime performance. When a skin is not active, the bones, constraints, and attachments associated with that skin are inactive and not processed. This means that only the elements of the active skin are calculated, which can lead to more efficient processing and improved performance. The metrics you see, such as "Bones: 52/65", indicate the number of active elements versus the total, showing that inactive elements are not being processed.

Ducky-Dee Welcome to the Spine forum!
Spinebot's answer is correct. Just to be clear, attachments are excluded from the calculation if they are inactive, even if they do not belong to a skin, so the result may not change much without using skins, but if bones and constraints are not included in any skin, they will affect the calculation even if the attachment they animate is hidden and the skeleton's appearance is not changed, so it is more efficient to include bones and constraints that are exclusive to a particular skin in that skin.
The number of slots has a negligible impact on performance.

For more information on how to see what is displayed in the Metrics view, see the user guide:
https://esotericsoftware.com/spine-metrics