What is the fastest way to mutually insufficient material for checkmate?

I mean the fastest way to a position in which each player has only the king left, or one of them has only one knight or one bishop left beside the king, or each one of them has only one bishop beside the king and both bishops are on a square in the same color, and therefore no one can checkmate. That excludes positions in which checkmate is still theoretically possible but cannot be forced by anyone like a position in which each player has only one minor piece beside the king other than the mentioned position.

https://www.chess.com/membership?c=no-ads and that’s the fastest way to get blocked 

From 32 men down to 4 men KB vs. KB (same color bishops) requires 28 captures.
You cannot capture on move 1 and 1 more none-capture is needed as well.
Thus 15.5 moves is the theoretical minimum.

Sam Loyd in the 19th century created a game that leaves only the two kings in just 17 moves. This record held for a long time, until 2000 when a problemist named Ponzetto did it in 16.5 moves.

#4

This ends with 2 bare kings, but it should be possible to shorten this by one move by ending with KB vs. KB with same color bishops, insufficient mating material.