I only needed one more item to “unlock extra savings up to 15%”, so I added an extra item to see what the savings would be. I didn’t think the savings matched what was advertised, so I removed an item to see what the difference was (making sure to screenshot before/after this time). Turns out the price of 3 out of 4 items is the same after an extra 5% discount.
You just need to be a good shopper. That’s why online is always going to be problematic.