Slow pageload, Thumbnails are built in activated turbomode

Hi there!

I am using Simple Image Gallery Extended Pro v 4.3.1.0. On Joomla 4.2.9 which is the latest versions by today.

In the syntax I have activated the turbo mode for every gallery:
{gallery}stories/komplikationer,turbo=1{gallery}

In the settings plugin I have activated "Cache thumbnails" and de-activated "Overwrite thumbnails"
Thumbnails size i specified in pixels and "Calculate maximum size of thumbnails" is deactivated.

In Modal view I hava activated "Show image information" and "Information from text file"
Watermark is activated and "Reset watermark" is deactivated.

I thought that these settings should result in quick pageloading but in fact i does not. It looks like the thumbnails are build during page load.
The turbo-text-file is build correctly.

Do you have any suggestions what I need to change in the settings to increase page load speed?

Thanks for your help
Niels