Unable to update calendar db to nc15

Nextcloud version 15.0.2
Operating system and version:

uname -a
Linux host 2.6.32 #3 SMP Mon Jul 23 11:24:42 CEST 2018 i686 unknown

Apache or nginx version Apache, Unknown version
PHP version 7.2:

The issue you are facing:

The calendar app is trying to add a column calendartype and index calobjects_index, but fails by too long index.
When trying to add calendartypeit doesn’t check whether it exists already, fails, and the update also fails.
I have tried to disable the calendar by setting enabled to false in appconfig, but to no avail.

Is this the first time you’ve seen this error? I have experienced the too long index before, but “fixed” it by creating the indexes manually.

I had problems updating with the web-updater, so have also tried occ upgrade.

The output of your Nextcloud log in Admin > Logging:

N/A

The output of your config.php file in /path/to/nextcloud (make sure you remove any identifiable information!):

config.php

<?php
$CONFIG = array (
  'instanceid' => 'XXX',
  'passwordsalt' => 'XXX',
  'secret' => 'XXX',
  'trusted_domains' => 
  array (
    0 => 'www.example.com',
    1 => 'cloud.example.com',
  ),
  'datadirectory' => '/home/sites/site34/clouddata',
  'overwrite.cli.url' => 'https://cloud.example.com',
  'htaccess.RewriteBase' => '/',
  'htaccess.IgnoreFrontController' => true,
  'dbtype' => 'mysql',
  'version' => '14.0.6.0',
  'dbname' => 'dbXXX',
  'dbhost' => 'mysql03.example.com',
  'dbport' => '',
  'dbtableprefix' => 'nc_',
  'dbuser' => 'user',
  'dbpassword' => 'XXX',
  'mysql.utf8mb4' => true,
  'installed' => true,
  'allow_user_to_change_display_name' => true,
  'maintenance' => false,
  'theme' => '',
  'loglevel' => 2,
  'updater.release.channel' => 'stable',
  'mail_domain' => 'example.com',
  'mail_from_address' => 'admin',
  'mail_smtpmode' => 'smtp',
  'mail_smtpauth' => 1,
  'mail_smtpname' => 'user@example.com',
  'mail_smtppassword' => 'XXX',
  'mail_smtphost' => 'mail.example.com',
  'mail_smtpport' => '465',
  'mail_smtpsecure' => 'ssl',
  'mail_smtpauthtype' => 'LOGIN',
  'enable_previews' => true,
  'updater.secret' => 'XXX',
);

The output of your Apache/nginx/system log in /var/log/____:

N/A