Extensions system in Opencart2+

I am starting to work on the switch from OpenCart 1.5 to OpenCart 2+ for 5 live shops.

I had half hopes that modification/extension system would be simpler to manage with the new version, but I'm starting to worry.

There are two different versions of vqModerator
https://github.com/vqmod/vqmod/releases
http://www.opencart.com/index.php?route ... e=JNeuhoff

One doesn't seem to install, the other one installs but I can't access the XML files.

And now there is another "Override engine" from JNeuhoff
http://www.opencart.com/index.php?route ... e=JNeuhoff
Now, this one just breaks the system on installation ( Notice: Cannot find system class file for 'library/currency.php' in C:\www\opencart-2.2.0.0\system\engine\factory.php on line 527 )

I have several (70+) vqmod modifications to switch from 1.5 to 2+. A few of them are entirely made by me for some specific clients
and I have a big commercial extension that I intend to switch too
http://www.opencart.com/index.php?route ... n_id=21956
(Category Manager, aka Category Tree for products)

Could someone please tell me if there is a way to switch from OpenCart 1.5 extensions to OC2+ extensions with a minimum amount of rewriting ? Which extension system should I use ?

If a few years of work on an OS project doesn't help the user to use it, I might have to call my losses and talk to my clients about WooCommerce ... :/

And now there is another "Override engine" from JNeuhoff
http://www.opencart.com/index.php?route ... e=JNeuhoff
Now, this one just breaks the system on installation ( Notice: Cannot find system class file for 'library/currency.php' in C:\www\opencart-2.2.0.0\system\engine\factory.php on line 527 )

There is indeed no 'library/currency.php' in OpenCart 2.2.0.0, it's now in 'library/cart/currency.php'. It looks like you are using a wrong, non-matching version of the Override Engine. This can be easily fixed by installing the correct one from http://www.opencart.com/index.php?route ... on_id=8588

There are two different versions of vqModerator
https://github.com/vqmod/vqmod/releases
http://www.opencart.com/index.php?route ... e=JNeuhoff

One doesn't seem to install, the other one installs but I can't access the XML files.

The Integrated VQmod lists all the VQmod XML files just fine.

You are not posting enough details here as to why you experience these problems, so we are unable to reproduce them.

There are considerable differences between the OpenCart 1.5.x and 2.x frameworks, so porting any extension from 1.5.x to 2.x will take some work.