Yes. Chess engines prune moves quite extensively. Chess programming is all about pruning.

When an engine says "search up to depth 15", it really mean depth as in iterative deepening depth-first search. It doesn't necessarily mean the engine attempts to search everything up to depth 15. It's complicated, but most of the bad moves would be reduced (or even eliminated), and a some critical lines variations extended beyond depth 15.

90% pruning is not uncommon, in fact it'd be more like 99.999999999% according to your definition.

Yes. Chess engines prune moves quite extensively. Chess programming is all about pruning.

When an engine says "search up to depth 15", it really mean depth as in iterative deepening depth-first search. It doesn't mean that the engine attempts to search everything up to depth 15. No good chess engine would search everything to depth 15.

It's complicated, but most of the bad moves should be reduced by depth (or even eliminated), and some critical lines variations extended beyond depth 15.

90% pruning is not uncommon, in fact it'd be more like 99.999999999999999999% according to your definition.