We have created a custom module in SuiteCRM 7.15 and export the installation zip from it.
Now, we want to install that module in v7.13 using module loader.
Will it work or crash our crm? 
Hello,
that is the question 
Do you have a staging environment to try it out first?
So far, I had very good experience when deploying modules cross SuiteCRM versions.
The only issues that I had so far, have been with PHP deprecations / PHP versions and deprecated custom code during module installation.
For things like this, Iād usually take a snapshot / backup and simply try it - in the worst case re-store things to a few minutes ago.
Did you see anything in the release notes about module builder changes?
Or just the PHP version bump?
I did not see anything in release notes related to module builder. I think it is good idea to create custom module in same version to avoid PHP errors.