Time required to visit another terminal at IAH
 

Next Tuesday I will be flying into IAH from LIR (Costa Rica), with a 2 hour 15 minute layover before continuing on to MSP. Both flights are United. As far as I can tell, we'll fly into Terminal E and could depart from any terminal.

We would like to visit the KLM lounge in Terminal D (have Priority Pass Select), and I'm wondering if there will be enough time and if there's any trouble traveling between terminals without a boarding pass for that terminal.

all terminals are connected post-security via an elevated tram. (This is not to be confused with the pre-security subway tram which also connects all terminals and the hotel.)

You can pass through the post CBP TSA checkpoint and then turn right and you are 2-3 minutes from the KLM lounge in D.

The elevated tram takes less than ten minutes to get all the way to A from D/E with the other terminal stops in between. Terminal C, E and D are all connected and walkable also.

Your big what if will be CBP times IMO unless you have Global Entry.