Say you have two metagenomic samples. You want to quantify the differential abundance of 15 genes between the two samples. What's the most straight-forward way to do this, while properly accounting for the sequencing depth of each library?
You'll have to find a normalizing gene, a gene that should have the same levels in both samples. It would be very hard to normalize otherwise. Another approach is to have conclusions in the form: gene A is more abundant than gene B in sample 1 (or condition 1) but less in sample 2. It would be much stronger if you'll look at pathways or modules etc.
In other words, you can use RTqPCR.
If it's just 15 genes of interest then sure, I was hoping he would want to get some more out of this data :)