Hmm, that really depends on the selected area.
Kurviger Pro 1.11.6
Android 8.0.0 (API 26)
samsung SM-G930F
1080 x 1920 (480 dpi)
all layers on
Map center near Tilburg Netherlands:
- 13.1 => perfect smooth
- 12.9 - 12.1 => ~1-3 fps
- 11.9 - 11.1 => nearly smooth ~10 fps
- 10.9 - 10.1 => ~3 fps
- 9.9 - 9.1 => ~10 fps
- 8.9 - 8.1 => ~5-10 fps
- 7.9 => perfect smooth
Map center near Utrecht Netherlands
- 13.1 => perfect smooth
- 12.9 - 12.1 => ~3-5 fps
- 11.9 - 11.1 => ~5-10 fps
- 10.9 - 10.1 => ~3-5 fps
- 9.9 - 9.1 => ~3-5 fps
- 8.9 - 8.1 => 3-5 fps
- 7.9 => perfect smooth
Please take the fps rates with a grain of salt, as I’ve estimated them, and the performance is not constant either.
But the zoom level thresholds should be very close 
Manfred