You definitely want to check, though a big hint is what the advertised speed is on the ride. If it's 10-12 m ph or something like that, then it probably really is a "no drop" ride becuase they're already going slowly. These are often truly social rides where folks cruise around and chat with each other.
If it's 14-ish or more (the higher it is, the more likely they'll drop people), then in my experience *some* people will hold to that "no drop" but it goes against all the other messages their bodies are sending to their mind when they're warmed up and ready to ROLL.
Your best bet IMO is to find somebody to go *with* you because you're more likely to be seen if there are two of you, and if you do get dropped you won't be alone. (Whenever I tried a faster ride I had at least two comrades and I tended to have overtrained for the advertised speed, which is not necessarily connected at *all* with the real spped.)
Another reality is that to have an "average" speed of 15 you spend (at least on this terrain) you have to be able to *cruise* for a time at 17-18.
So, the answer is [like anything else] "It Depends!"