Reproduce: 1. Select an item on the desktop 2. Hit the DEL key 3. Nothing happens... 4. ...after about 300ms the item disappears without further confirmation.
What sort of confirmation do you expect exactly?
I can confirm the strange delay (it's fast via the context menu so it has to be possible to improve it somehow).
Expected sort of confirmation: same as in dolphin, I would suggest. In dolphin this behaviour is configurable in the Confirmations tab of the General category of the Preferences dialog. (On a side note, with dolphin 15.07.90, this seems to be broken: I got no confirmation regardless of the setting)
Turns out the speed diff I perceived doesn't really exist after all - I was accidentally comparing Delete and what Del does in Folder View (Move to Trash). They're equally fast otherwise and the same speed as Dolphin, so if that's too slow it's really down to KIO::trash(). The code also does a askDeleteConfirmation() so it's settings-backed.
I still have the issue. I'll try again with Plasma 5.5.