Here's a solution that doesn't require fudging with `SUBSEP`, looping through the fields, having the files being pre-sorted, or have a pre-set number of columns/fields : 

 mawk -v \_=testfile_001.txt -F/ '
 BEGIN { 
 while(getline<_) {
 __[$!(NF=NF)] 
 }
 _*=close(_)*(FS="^$") } _^($_ in __)' testfile_002.txt 
 
 0 14
 0 15
 0 20
 7200 14
 7200 15

* just realized setting `FS="^$"` for **2nd file** is much faster since we're doing line-wide matching, so `splitting fields` is a waste of time.

Tested and proven working on `gawk 5.1.1` (including flags `-c/-P`), `mawk 1.3.4`, `mawk 1.9.9.6`, and `macos nawk`

-- `The 4Chan Teller`