I tried to find a nice photo collage frame for only a few 10x15cm photos but I did not find an adequate frame. Then I saw the cheap IKEA NYTTJA frames which are perfect for my intention.
The seven NYTTJA frames are screwed together by giving some of them an angled position. The space between the frames have to be selected to be able to put in the photos from the backside.
A hanger is added to the frame after putting all elements together. Afterwards, it can be filled with some nice photos from my trips.