That’s going to be a tough one. Especially if you want half-way decent accuracy.
Given the premise you get what you pay for, you’re automatically limiting yourself to components that aren’t the best choice for the job.
The 1115 has a max sample rate of ~800 samples per second. i.e. it’s too slow.
Forum user ybizeul tried and found out the hard way…
See this thread: ADS1115 and sampling speed - #2 by Robert.Wall
The picture in post #23 of that thread shows what happens to the waveform when it’s sampled at such a slow rate.