Problem/Motivation
PHP 7 complete's test runs 1/3rd faster than PHP 5.6. This saves overall resources for the testing infrastructure, as well as giving quicker feedback to patch authors.
https://dispatcher.drupalci.org/job/php7_mysql5.5/133/ 21 minutes.
https://dispatcher.drupalci.org/job/php5.6_mysql5.5/173/ 30 minutes.
Also in general I think we should emphasise support for the most recent stable PHP version
Proposed resolution
Default patch testing to PHP 7, switch PHP 5.5 to per-commit testing.
Do this as soon as PHP 7.0 is out or when the two testing hacks in #2454439: [META] Support PHP 7 have been reverted.
Remaining tasks
Decide that we're going to do it, then postpone on #2454439: [META] Support PHP 7.