Graphing Dynamic Data

Need feedback how to handle
this challenge within Zoho
sheet:

I have a range of numeric
data which is incremented
by (1) row from a daily API
pull.

The API always returns the
data in descending date order
(most current dates first).

Each row consists of a date
MM/DD/YY) & a count (NN)
field in that order.

My calculation process requires
the I sort the entire range by
oldest dates first, then skip the
first 15 rows and then calculate
(5) additional columns.

The last column and the original
date column are subsequently used
to produce a line graph.

I've tried linked cells and manual
sorts, but the requirement to skip the first 15 rows based on a dynamic range has me stumped.

I don't believe Zoho sheet has a
macro function to do the range
sort & skip 15 rows - so how could
I solve this challenge using perhaps a staging and production
worksheet approach.

Please confirm.

Thanks
imalr