QtCreator really slow including Eigen library

When I updated to Qt Creator 3.5.1 I noticed that it was really slow.
Code highlighting, auto completion were slow and Ctrl+Click, F2 were making Qt Creator hang for a few seconds.

The issue https://bugreports.qt.io/browse/QTCREATORBUG-14860 looked like the same thing, but it wasn't. I tested with 3.5.82 but the same problems remained.

I decided to bisect my git repository and found out that this line on .pro file was making it all slow.
INCLUDEPATH += /usr/include/eigen3/
By removing it, eigen files were not included at all.
Qt Creator before 3.5.1 was usable but I had a feeling that it was a little bit slow.
After 3.5.1, Qt Creator became almost unusable as it had no auto completion and constantly hanged for a few seconds. This is why I marked this as a bug.

This is the Eigen library: http://eigen.tuxfamily.org/index.php?title=Main_Page
It's worth saying that it uses a lot of templates.

EDIT: Making a few more tests, I've noticed that just by including eigen files it gets slow.