There are various things you could try — including using the Tile feature in the Print dialog box. But I think the easiest thing to do would be to make a new 15 x 10cm document, add a graphic frame, and then place the original INDD file into it at 100% size (cropping to the part you want to see). Yes, you can place an INDD into another INDD file. :-)

Then you can print and see how it looks!

I think perhaps you want to look at the free AutoFit plug-in from Typefi. It’s pretty amazing.
See:

How to Create the Effect of Different Strokes on the Sides of a Frame

and
https://www.typefi.com/products-services/design-tools/autofit/

WOW! Thank you, Peter. Great solution to use Conditional Text. I haven’t tried it yet. But for anyone here who does not know about conditional text, here are some resources:

InDesign How-to: Use Conditional Text

and

Unexpected Uses for Conditional Text