I have not vacuumed the gravel since i started the tank, i have just done a few water changes. I use to have 4 small blood fin tetras in the tank, removed them and now it is shrimp and snail only.
How long have you had the tank?
If a significant amount of time, you probably have a ton of mulm down there they are hunting through. If you can vacuum the gravel it will slow down their multiplying. Just don't vacuum too much at once. There's likely a lot of beneficial bacteria in there that would be good to keep. If you have had the tank over 5 months, I would recommend only vacuuming either 1/4 of the tank every two or three weeks the first time, until you've cleaned all of it. OR clean all of the top, but don't clean deep down. The snails will go deeper, continue to multiply, but eventually, if you vacuum the top every few weeks, they will run out of food and shrink in numbers.
If you don't mind them being there, consider them garbage collectors. If you dislike them, you can do a few things to get rid of them. The most natural being a combination of cleaning the gravel as suggested, capturing them with bait sometimes works, and others just reach in and smush them, or throw them in the trash every time they see them, until they're pretty much all gone.
Any kind of chemical or medicine you might use to kill off the snails would likely kill your shrimp though.
You could also get assassin snails, though I'm not sure how effective they are with MTS, they eat other snails.