8 was the first version to support frameworks. (IIRC) You would need at least 8 and have to compile a 32 & 64-bit version of the framework. There are some interop annoyances around the size of ints in iOS when interfacing with Kotlin code when trying to use the same code for 32 & 64 bit.
That said, the 5c is in Apple's obsolete category. They don't do any repairs on them anymore. Most, if any devices that are locked in to iOS 9 should be obsolete or nearing it by now.