I was wondering if you could clarify some details about your setup:
How long is the video layout you want to show every 15 minutes?
Do you want the 2 hour layout to resume from where it got to in the playlist after each 15 minute video layout?
What player type are you using and the player version? If you are unsure, go to the Displays page in your CMS, click the Column Visibility button and select the Version column. What does that column say for the display you want to set this schedule up on?
On a side note, I noticed you mentioned you are using CMS 2.3.6. That release is not secure, I would recommend upgrading to 2.3.17 or newer. Here is official blog post about that issues, if you want more information.
client software - Windows 7\10 - xibo-client-v2-R256.7
general layout - about 2 hours (for example). There are different video files of different durations.
videos for “insertion” - from 30 seconds to 2 minutes.
I just don’t understand how to insert them, for example, as a separate layout so that it plays on top of the current one.
In the schedule settings, if you set the repetition 4 times (for example), then it repeats them one by one, and does not break them up within an hour)
Currently all scheduled layouts are designed to show the entire layout, not just a specific media item from that layout each time it shows. It’s an interesting use case, I would recommend creating a feature request for your use case, so the developers can discuss it and decide whether new functionality will be added to a future release.
I’m sorry I don’t have another solution I can offer.