Since the "Ranking the Teams" thread is unspoiled and I can't find any other threads for this, I decided to place my calculations, based on theschnauzers's numbers, here.
Jet-Cord   2.8750   23/8   
Carol-Brandy   3.8750   31/8  
Louie-Michael   4.5000   36/8  
Jordan-Daniel    5.5000   44/8  
Brent-Caite    5.5000   44/8   
Steve-Allison   3.3750   27/8
Jeff-Jordan   5.6666   34/6
Joseph-Heidi    4.4000   22/5   
Monique-Shawne 5.3333   16/3
Jody-Shannon    10.0000   20/2
Adrian-Dana    11.0000   11/1   
- Carol & Brandy are currently 31/8.  Since they're expected to go this week, they'll end up with 36/9 --> final average placement of 4.0000  
 - Louie & Michael are currently 36/8.  With the spoilers pointing to back-to-back 4th place finishes in Shanghai, they can't do any better than 45/11 or 4.0909.
 - Jordan & Daniel and Brent & Caite are both currently 44/8.  Neither team can do better than 48/12 or 4.0000.
 
I learned my lesson, from the sums of all the final 3 and final 4 teams, that trying to determine the best and worst performing casts with just average placements doesn't work.
I think the only way to compare the casts of each season is to determine if that particular cast has reached certain benchmarks. 
If TAR16 shakes out the way the spoilers indicate, then I will argue that the TAR16 cast is indeed the worst performing cast in TAR US history based on at least 3 different benchmarks:
-  Every cast from TAR1-TAR15 has had at least 3 teams with an average placement better than 4.  TAR16 looks like it's going to be the first cast to not accomplish this, with only Jet & Cord and Steve & Allie doing better than 4.  
 -  No cast from TAR1-TAR15 has ever had more than 1 team in the final 4 with an average placement of 4 or worse.  TAR16 looks like it's going to end up with 3 teams in the final 4 with an average placement of 4 or worse.
 - No cast from TAR1-TAR15 has ever had more than 1 team in the final 3 with an average placement of 4 or worse.  TAR16 looks like it's going to end up with 2 teams in the final 3 with an average placement of 4 or worse.
 
Eric & Danielle are the worst performing winners right now with 3.6153.  If Jet & Cord don't win, TAR16 will have the worst performing winners in TAR US history, and it will also have the first winners to have an average placement of 4 or worse.
One last item of note is that every winner has had an average placement ranked either first, second, or third compared to everyone in their own cast, except for Eric & Danielle whose average placement was ranked fourth in their cast behind Oswald & Danny, Rob & Amber, and Dustin & Kandice.  If Jet & Cord don't win, TAR16's winners could rank anywhere from third in their cast, tied with Carol & Brandy, all the way to sixth in their cast.