I've had two vaginal deliveries and each time the epidural has worn off. My first delivery I could feel everything on one side and the epidural was reinserted. The second delivery an epidural was placed and it wore off maybe after an hour, then I was given two more through an IV with no relief. I've also had long labors, my first was 15hrs and the second 17 hrs. If I were to have another child would I potentially have an even longer labor without any relief?

Were these both done at the same location? While most women are satisfied with their epidurals, others are not. Placement, the medications used, and how you respond to them, and what sort of epidural you have are the main reasons an epidural may be limited or not take at all for some women.
I would see about finding out the specifics of your previous experiences with it and be sure to go over the options available to you if you become pregnant again.

Generally subsequent labors move along more quickly... but this does not hold true for everyone. Some women naturally having longer or shorter labors than others. Choices in labor, such as positioning, the level of support you have, and medication use, can play a role in the length of labor. Having an epidural itself can sometimes cause a longer labor and second stage for some women.
Definitely look into the many options you have for pain relief to help you until you get to a point of having an epidural if you decide to have another one.

I'm curious as to how long ago this was.

Most epidurals are now on a pump. That pump gives a continuous dose of medication for approximately 13 hours before it has to be refilled.