Since there seems to be some disagreement about who the Texans played based on a Box Score, I actually went to Twitter and pulled snap counts. Based on that, I found that all of the Texans' defensive starters did indeed play with the exception of DT Sheldon Rankins, LB Christian Kirksey, and S Jimmie Ward. Their other starters all played around 20% of the snaps.
After that, their second string defense was a mix, but since we're mostly worried about the Pats OL, I focused on Houston's DL - their second string played a solid 30-50% of the snaps after the first string left depending on the player, which puts us into the 3rd/4th quarter.
Compare that to the below snap counts for the Pats OL:
First string:
Brown: 0%
Strange: 0%
D Andrews: 0%
Onwenu: 0%
Reiff: 0%
Second string:
Anderson: 0%
Murray: 0%
Ferentz: 81% (he must've played some LG for this to make sense)
Russey: 46%
McDermott: 0% (at right tackle)
Third string:
McDermott, I guess: 52%; Steuber: 60% (assume he played LT for the snaps to make sense)
Mafi: 27% (lower than I thought)
J Andrews: 73%
Hines: 73%
Sow: 88%
As you can see above, a majority of the game was Houston's first or second string DL against McDermott or Steuber at LT /Ferentz/Jake Andrews/Russey or Hines/Sow. Hopefully that explains why it looked like ****.