MacTeX 2015 running much slower than MacTeX 2014?

Question

I just installed MacTeX 2015 on OS X 10.6.8, and it is typesetting significantly slower than the 2014 distribution; for one particular file, 2014 will typeset it in 11 seconds, but 2015 takes 77 seconds (!). Has anyone else had this problem? If not, any ideas on what might cause this? Thankfully, MacTeX added a Preferences pane that makes it easy to switch back to old versions.

/Library/TeX/texbin is still in my path, the TeX file in /etc/paths.d points to the same thing, and the texbin in /usr is also from the 2015 install. I'm not sure what would need to be changed if the path is the problem.

The slowdown occurs with all the files I've tried, but here's a relatively short one that shows quite a difference: http://freitag.creighton.edu/Example.tex

This runs in about 4 sec. using 2014, but 35 sec. using 2015. Using 2015, it hangs between the lines

(/usr/local/texlive/2015/texmf-dist/tex/latex/latexconfig/epstopdf-sys.cfg))

and

[1{/usr/local/texlive/2015/texmf-var/fonts/map/pdftex/updmap/pdftex.map}]

in the console, although that's not the case for all the files I've tried.

Answer 1

The mhchem package v4.x is very very slow! In your file (Example.tex), you may try to replace:

\usepackage[version=3]{mhchem}

by the following lines (and use a faked \ce macro):

\usepackage{amsmath}
%\usepackage[version=3]{mhchem}
\newcommand\ce[1]{\ensuremath{#1}}

As you use mhchem v3 features, you may download and use an old version of mhchem (v3.21):

https://www.tug.org/svn/texlive/trunk/Master/texmf-dist/tex/latex/mhchem/mhchem.sty?revision=36504&view=co

Here, you can compare durations of compilation:

mhchem v4.01    => 13.0s
mhchem v3.21    =>  1.7s
faked \ce macro =>  0.2s