David Mooney's goal put the visitors on course for victory, but Proschwitz earned a replay by heading home in the fourth minute of stoppage time.
"We can't be any worse playing down at Orient than we were playing out there today," Bruce said.
"It was absolutely awful. Were there any positives? Well, it did not rain. Only three players - the two central defenders and the goalkeeper - came anywhere near to producing what they can, and the rest did not.
"The one thing you can say is that a lot of the players need more games, as a lot haven't played recently.
"However, we had an experienced team out there on the pitch and they just did not perform at all.
"If I'm honest it's a replay we could possibly do without, but we're still in the draw and still in the FA Cup."
Orient manager Russell Slade said: "We were positive but it was the manner in which we were disciplined and organised that pleased me.
"It was probably one of our best performances of the season. We created a few chances, but we didn't have loads of problems defensively and that was the most pleasing aspect."