Magento 2 – Fix Slow Routers_Match

1.4 to 1.9 is a big jump, you are probably simply going out of computational resource and you need a better hosting.

If you want to make more tests on disabling extensions just make sure you are turning them off by modifying the xml files in app/etc/modules. JUst open the extension you wish to disable and set <active> tag to false. Manually flush the cache at each step by removing the content of var/cache directory (do NOT remove the cache folder itself).

If you get errors after disabling a module just turn it back on to fix.

Disabling from backend only disables their output, but they remain active.

Also check your cache engine, using Redis may result a in good performance boost.

For frontend you can use MSP LTS2 Full-Page Cache module: https://github.com/magespecialist/lts2

If you already did this, please make a better profiling with AOE_Profiler: https://github.com/AOEpeople/Aoe_Profiler

The amount of JS is huge, but if it sums up to 8MB there's something wrong. You should use the "Bundling" configuration in production mode if you don't want >100 files loaded.

With the default Luma theme, bundling, merge and minify enabled, the bundled JS file is 1.9MB.

Varnish is another topic and won't help with performance of generated static files.