Just to give you a sense of the currents based on 2 of 6 dives that I did there in 1998 (yup, back when there were whalesharks at Richelieu Rock): on one dive, we dropped in away from the Rock and started heading towards it, following the dive guide. Many of the divers wanted to go to 90+ feet to see a seahorse that I had already seen on the previous dive. So I stayed at around 50 ft. to conserve air for chasing Mr. Big, and told the dive guide and my buddies - they were OK with that.
The divers below me were barely visible (due to both the poor viz and the bubbles), so I started following the bubbles instead. At some point in time, the bubbles became less and suddenly I had nothing to follow. I was in the blue with no reference - couldn't see the bottom and couldn't see the Rock. So I surfaced and saw the Rock about 150 ft. away, took a compass heading, and went back down to about 15 ft. and kicked. And kicked....but still no Rock in sight. So I surfaced once again and now the Rock was 600 ft. or more away - my heading was correct but the current just took me away.
Now, I don't know how Richelieu Rock is nowadays but back then there had to be at least 10 dive boats crisscrossing those waters - not the best place for a diver to be, bobbing on the surface. Hopefully you have a sausage and/or other surface signaling device.
I also recall vividly my last dive there when we were all hanging on to the Rock at about 15-20 feet waiting for the whaleshark. Everyone was fully extended horizontal, waving like flags.
Two things that you ought to get from this:
(1) Currents will vary, and while some people might dread diving in any current, keep in mind that it is the currents that bring about the life on the reef: the coral polyps open up in their greatest splendor and there is a lot more fish activity. So do not view current as being your enemy, altho at this stage, understandably you might prefer that it not be strong. In fact, you could get lucky and experience little or no current, but remember that conditions can change from dive to dive. Do you really want to depend on luck?
(2) currents tend to be strongest as you get closer to the surface. If you can't get down as fast as the rest of the divers, in a worst case scenario, you may lose them or they may lose you. In either case, you may wind up in the blue all by yourself like I was, in boat-infested waters - which can sometimes be harmful to your health.
Richelieu Rock remains one of my favorite dives ever. Even without whalesharks, there was so much else to see. I think that it can be more enjoyable if a diver doesn't have to worry about current, equalization, air consumption, etc. Hopefully by the time you get to Richelieu Rock, you will have overcome these issues. And if you still need to descend slowly, definitely tell the dive guide so that he keeps an eye on you and doesn't leave you behind.