mass price change for all products in a specific category

[Altair]

If all of those Products use that Category's categories_id as their master_categories_id ...

You can backup your database and then run:

UPDATE products SET products_price = products_price * 1.15 WHERE master_categories_id = XX;

where XX is the master_categories_id for these Products ...

Then, go to the Tools ... Store Manager ... and click admin/store_manager.php, and run the:

Update ALL Products Price Sorter
 to be able to sort by displayed prices: Update