Upgrade to 15x

On 2018-05-01, http://wiki-translation.com was upgraded from Tiki 12.x to 15.x

On 2018-05-14

• "Wiki URL Scheme" was changed from from spaces with + to - (which is the default in 18.x)
• http://next.wiki-translation.com is set up to test upgrade as per https://tiki.org/Pre-Dogfood-Server
  • user: next
  • password: next

See old notes about Upgrade to 12x