Looks like all the icons for all the themes are downloaded (once?) when reittiopas is accessed.
Based on MOMS/piwik stats:
So during a period of one week each unique user has on average downloaded 6,67MB worth of icons with an average of 216 http requests.
In addition to the fact that unneeded icons are downloaded some of the icons are also unnecessary large, for example this: https://www.reittiopas.fi/icons-oulu-4b3f1eb554f4fedc9e560a25d091cb10/apple-touch-startup-image-1496x2048.png
The size is roughly 170kB
Do we need icons of size 1496x2048 pixels?