In Collections, after importing BT15 and adding 5 single cards (different BT15 cards from newer sets) and entering exit mode to update quantities there was significant delay (approximately 3s) per increment on card.
Only a few days ago I was able to increment card quantity without issue.
If this is caused by a change to minimize individual database transactions, it might be worth investigating "edit mode" with "save and exit edit mode" that writes all changes from the edit session and refuse to exit "edit mode" on a failed update/write to the database