Bug with biber 2.15 under Windows with large bib-files

I just updated my MikTeX distribution and am now running biber 2.15 with biblatex 3.15a. And all of a sudden, I run into problems. I have a bib-file with 1888 entries, and trying to use that now seems to break biblatex, although it worked fine on earlier versions. I do not know if the problem lies with biber or biblatex, but try the following:

I created two bib-files out of my original one, available here and here. With the following MWE it works fine and both citations are resolved:

documentclass{article}
usepackage[french, german, UKenglish]{babel}
usepackage[backend=biber, style=authoryear]{biblatex}
addbibresource{Test.bib}
addbibresource{Test2.bib}

begin{document}
Let's test: textcite{Arnold2002}, textcite{Setty1973}

printbibliography
end{document}

However, when I combine both bib-files into one and try to compile with that, none of the citations is resolved. Since it works fine when having the database split in two, I cannot see any other reason for this behaviour other than the new biber or biblatex having a limit of file-size/entry-number in the bib-file. Not the amount of entries actually cited, mind you (as it was in bibtex), but the sheer number of entries in the database. Or do I overlook something? Any help would be greatly appreciated.

EDIT 1:

Here is the .blg-file. Indeed, there is an error message "[1095]", but I cannot make sense of it:

[0] Config.pm:312> INFO - This is Biber 2.15 (beta)
[0] Config.pm:315> INFO - Logfile is 'DatabaseTest.blg'
[311] biber-MSWIN64:330> INFO - === 
[385] Biber.pm:415> INFO - Reading 'DatabaseTest.bcf'
[882] Biber.pm:952> INFO - Found 2 citekeys in bib section 0
[998] Biber.pm:4334> INFO - Processing section 0
[1068] Biber.pm:4523> INFO - Looking for bibtex format file 'TestFull.bib' for section 0
[1095] Utils.pm:411> ERROR - Data file 'TestFull.bib' cannot be read in encoding 'utf8': Wide character at C:UsersManueAppDataLocalTemppar-4d616e7565cache-b32225defac3568d1e921af5a7245ca571b236aainclib/Win32/Unicode/File.pm line 163.
[1095] Biber.pm:132> INFO - ERRORS: 1

EDIT 2:

I now identified the limit length. The file available here contains as many entries as I manage to process. It contains 1477 entries, 25026 lines, and 1,048,339 bytes. This file just works, but as soon as I add just one more mock entry like

@Article{Test3,
  author       = {Author, A. and Author B. and Author, C.},
  date         = {2020},
  journaltitle = {A Journal},
  title        = {A nice title of a certain topic which I cannot even imagine},
  issue        = {3},
  pages        = {1--18},
  volume       = {12}
}

I get the same error as above. This seems to be the length limit with which biblatex works properly.

EDIT 3:

Here is the full file that does not work directly from JabRef (as .bib) without any changes. And here is the same file as hex dump exported with Cygwin.