I received a letter from Stenger & Stenger P.C. for a Motion to Dismiss Proceedings Supplemental. What does that mean?

That's a good thing. Proceeding Supplemental is what the creditor wants to get you to come to Court, and testify as to your funds and assets in order to garnish your wages, take your assets, etc. Motion to Dismiss it is actually creditor asking the Court to cancel that proceeding supplemental for now. It could be for now, it could be for a while, or forever - no one knows except the creditor and their attorneys. Does not guarantee that there won't be another Proceeding Supplemental, but for now, this one is requesting the Court to cancel it.

Generally a proceedings supplemental occurs when you have already been sued and there is a judgment for money against you.
If they bought this debt and its past the SOL, then did you defend? Did you file an answer asserting SOL as a defense? Where is this procedurally?
As far as a dismissal of proceedings supplementary, it could be because they either do not think you have something, or they already know where they are going to levy, and probably are looking for a wage garnishment or bank garnishment.
Click on "Find a Lawyer" above and locate a debt collection defense lawyer in your area to assist you. This sounds like an interesting case. I note, too, that LVNV got snagged by the CFPB recently and I think they settled agreeing to dismiss a ton of cases.

Just wanted to correct you on one statement. If LVNV Funding already has a judgment against you, that means that the SOL has been waived by you in defending the case or that they got the judgment against you by default. In Indiana, a judgment is good for at least 20 years from the date the judge signs it. So, just because they are asking the court to dismiss the proceedings supplemental doesn't necessarily mean that they won't come after you later.