Yes there are going to be issues with three people testifying about speed which is why I suggested a 50/50 chance of it working. What they say and how they say it will be important to the JP's decision. If it was just the driver testifying himself then the chances are pretty much 0 that JP will believe driver over officer. Add a couple more witnesses though, and maybe (MAYBE) JP will believe them.
The op agreed he was speeding about 15 over but was not speeding at 49 over so that was the issue was trying to bring the speed down.