Dear Puybaret, Gildaniel,
thank you for your replies and hint that I can further narrow down the issue.

I tested three SH3D versions
A) SH3D v6.4.3 (from MS Store), Java v1.8.0_202 64bit, Java 3D Version 1.6.1
B) SH3D v5.5a, Java Version 1.8.0_144 - 64 bit, Java 3D Version 1.6.0
C) SH3D v5.4, Java ...

Sorry for the many posts. I really want to support the issue resolution as I appreciate the potential of SH3D very much and would like to use it properly.

I think I could narrow down the issue to the settings / the used version of Java.

I installed several SH3D windows executable files from here ...

Additional information / tries to narrow down the issue [2]:

7) Installed the SH3D v6.4.2 32bit version --> no impact.
Source of idea: http://www.sweethome3d.com/support/forum/viewthread_thread,7640_offset,80

8) Installed an old verison of SH3D: v4.6 with java version 1.6.0_45, 64bit ...

Additional information / tries to narrow down the issue:

1) I tried it with another computer --> no major improvement.
[I tried to link a snapshot picture to mediafire and imgbb but both didn't work here]
2) I exchanged the floor texture with colors --> major improvement
[I tried to link a ...

Dear SH3D community,
I really hope you can help as after hours I'm not able to solve the problem by myself. [:(]

Problem:
- 2D view is strongly lagging (0.5 - 1 second delay)

Other observations:
- 3D view works fluent like a charm
- SH3D consumes 1.2 GB of RAM (the sh3d-file is only 1.25 MB ...