1. Ubuntu 15.10 is unavailable at the moment (30.01.2018 - see attachement - available_boot_disks.png)
2. "Before you click Create, you need to do one last thing. Click on "Management, disk, networking, access & security options" which will make expand to show some new options. Then under "Access & security", scroll down to the section called Cloud SQL and change the drop-down from "None" to "Enabled"."

It's moved to "Identity and API access"section. Under "Set access for each API" radio button in "Access scopes" group. (see attachement - cloud_sql_api_access.png)

Src:
https://livebook.manning.com/#!/book/google-cloud-platform-in-action/chapter-2/v-10/90

3. Since Ubuntu 16.04, PHP 7.0 has replaced PHP 5.x and become the default version of PHP in the official Ubuntu application repository.

I used the following command:

sudo apt-get install apache2 mysql-client php7.0-mysql php7.0 libapache2-mod-php7.0 php7.0-mcrypt php7.0-gd

Src:
https://livebook.manning.com/#!/book/google-cloud-platform-in-action/chapter-2/v-10/103