15 x 10 is a really big stone. It's a long slow ureteroscopy that takes several hours as opposed to 20-30 minute quick dusting. We either dust a stone and literally turn into sand or we break it up into pieces and pull the pieces out with a stone basket. That's going to create a lot of stone burden. Some stones are really hard and don't break easily. It's rare the laser breaks but it is equipment and I have had it fail. Probably 2-3 times in 20 years. Many large hospitals have extras. I think we have three. Many small places rent them and as such the rental guys may only have one on the truck because their others are at other facilities.
Baskets can have several things go wrong. They can grab a stone too big to remove and thus get stuck. A piece can fragment off the basket and then you have to try to retrieve that. Visualization is poor because of how much stone dust is created from a large stone.
In summary, you and your surgeon had a bad day. Sometimes it doesn't go well. We've all been there. Lots of factors- where stone was located (in the kidney), large stone size, and it sounds like your ureter wasn't dilated. When you put a stent in, the ureter dilates and so we can run cameras up more easily, get bigger stone pieces out, etc. That's why it's easier on the 2nd go. Overall it sounds like they did the right thing and bailed out before more went wrong or you got hurt from the procedure.
It's likely you'll meet your deductible and both procedures will be covered. Watch your bills. If the insurance rules the 2nd surgery as medically unnecessary and not pay any of it (rare). The hospital can work with you on cost since it was at least partially due to equipment failure.