Yes! It is possible to manipulate with regular prices of woocommerce products, and change products price value related to their current value.
- Select products using checkboxes or filter them by any parameters you need
- Open Bulk Editor form
- Find field 'regular price' and check it by checkbox near
- Enter 15 in the textinput and in the drop-down near it select 'increase by %'
- Click on 'Do Bulk Edit' and wait while the operation finish