rode 15 miles in about two hours and was tired and sore for a week.
We have saying here: itīs not the distance that kills you but the speed.If you had taken it a bit slower and rode that distance in, say three hours, you would perhaps not been so tired and sore.
This is my 3-gear bike:
https://www.pyora-pori.fi/WebRoot/vilkas..._sininen_ml.jpg