This one:

sudo apt-get install libqt5serialport5 sudo apt-get install libqt5serialport5-dev

Solved the Issue for me.

That's an unusual folder. You can try to run your application with:

LD_LIBRARY_PATH=/usr/local/lib/arm-linux-gnueabihf ./your_application_name

Perhaps it's the problem ! Thank's for your time lucas and your work !

I also tried this on my Win7 machine but never succeeded. In the end I did a local compile on my RPi2 of Qt5.5. It compiled for 1041 minutes but is working nice now. I followed this guide for the local build. Instead of 5.4.1 I just got the latest source.
Could also be an option for you.

Well, that was a good idea !

You're welcome !

Since you have it working now, please mark the thread as solved using the "Topic Tool" button so other forum users may know a solution has been found :)