Probably not related to your issue, but here's how I am currently getting away using an old 3rd gen iPad (for testing one of my apps). The sounds work even though the system is something like iOS 9.3 (can't update any further cause the hardware is ancient). So this is how...
I'm using C3 with C2 runtime (advanced settings). Import sounds as m4a files. (You should be able to convert wav files with C2 (if you own it that is, if not Audacity should do the trick; import to C2 and export project to web/html, then locate media folder to grab them). When exporting to html, choose minify mode: simple (none doesn't seem to work; haven't tried advanced), leave the two boxes unchecked to be sure to have it the same as me (deduplicate and recompress unchecked). You can't use features meant for C3 runtime (such as the new functions), so this only works for simple projects.
C3 will convert the project to C3 runtime every time you launch, so be sure to go to advanced settings to change it each time you start working.
Oh almost forgot, preview doesn't work. To test, I need to upload all files to my own server.