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 Version 1.6.0_51 - 64 bit, Java 3D Version 1.6.0
with two demos
1) userGuideExample.sh3d
2) SweetHome3DExample13-AlpsHotel.sh3d

Outcome of the combinations:
A1: 2d view is lagging approx. 0.2 seconds [:(]
A2: 2d view is lagging approx. 1.5 seconds [:((]
B1: 2d view is lagging approx. 0.2 seconds [:(]
B2: 2d view is lagging approx. 1.5 seconds [:((]
C1: 2d view is NOT lagging - it works smooth [:)]
C2: 2d view is NOT lagging - it works smooth [:)]

The issue starts with SH3D v5.5a. There was a jump from Java 1.6 to Java 1.8. It seems that there is an issue with SH3D/Java to efficiently render textures in the 2D view starting with SH3D v5.5a until now v6.4.3.
Any thoughts on how we can overcome or more narrow down this issue are highly appreciated?