Godwin's cavalry was not part of the 15th Confederate.
Captain Alexander Godwin raised a small, independent cavalry company at Campbellton in northwestern Jackson County, Florida, during the summer of 1864. These men chased deserters, etc.
On September 26, 1864, they turned out to oppose approaching Union raiders under General Alexander Asboth and skirmished with him around Campbellton.
On September 27, 1864, they fought in the Battle of Marianna.
After the battle, some of the members were absorbed into other units, primarily Captain Robert Chisolm's cavalry which soon was rolled into the 5th Florida Cavalry as Company I. Others remained under Godwin's command.
Many of these men had earlier served in other Confederate units, but had been discharged due to wounds or for other medical reasons.