Don't know how United works and their staffing levels at BRU but with Delta it happens when you check in, elites and Delta One passengers may use the seperate SP line, took me 10 minutes to drop my luggage off, answer the 2-3 questions and get my BP.
After that you walk to the gates, go through security (using the fast lane), go through passport control and head to the gates (or lounge) were probably for the connecting pax there are those people asking the security questions again.

Took me like 25 minutes from arriving at check-in to the lounge (and that one was pretty close to the departure gate).
However since OP is connecting and most likely already has a BP, OP probably can walk straight to security.