Hello Gaaviya,
Welcome to the forums!
This is a hard question because there is no perfect answer. This is a balance between keeping more samples and keeping more reads from each sample. The good news is that 3.2k or more reads per sample is pretty good, and I've seen papers published with fewer reads.
Chris has an excellent explanation about how to use the Sampling Depth tool to see which samples from your various cohorts will be lost at a given depth threshold so you can make an informed decision for your data set.