batch as 15 minutes in YAML for Build pipeline

Question

I am creating a Build pipeline in Azure Devops (earlier VSTS), and want build to get triggered in BATCH every 15 minutes. If no merge received in repo then no build should be created.

Below is what I am referring to

trigger:
    batch: boolean # batch changes if true, start a new build for every push if false
branches:
    include: [ string ] # branch names which will trigger a build
    exclude: [ string ] # branch names which will not
paths:
    include: [ string ] # file paths which must match to trigger a build
    exclude: [ string ] # file paths which will not trigger a build code here

This code snippet I took from https://learn.microsoft.com/en-us/azure/devops/pipelines/yaml-schema?view=azure-devops&tabs=schema

trigger:
    batch: true
branches:
    include:
    - master

pool:
  vmImage: 'Ubuntu-16.04'

variables:
  buildConfiguration: 'Release'

steps:
- script: dotnet build --configuration $(buildConfiguration)
  displayName: 'dotnet build $(buildConfiguration)'

1. Only if I receive a merge in current repo NOW then all rest merges in current repo in another next 15 min would be part of same build. How to add 15 min detail in my YAML document?

2. After current build is Complete and until next merge is received in repo, 15 minutes time should not START? How do I code this in my YAML document?