That's easy... I have a 2.9 site sitting on my Ubuntu 16.04 dev box.
Login page...
Deprecated: Methods with the same name as their class will not be constructors in a future version of PHP; auth_plugin_manual has a deprecated constructor in /var/www/moodle29/auth/manual/auth.php on line 38
Deprecated: Methods with the same name as their class will not be constructors in a future version of PHP; auth_plugin_nologin has a deprecated constructor in /var/www/moodle29/auth/nologin/auth.php on line 32
Deprecated: Methods with the same name as their class will not be constructors in a future version of PHP; auth_plugin_email has a deprecated constructor in /var/www/moodle29/auth/email/auth.php on line 32
Deprecated: Methods with the same name as their class will not be constructors in a future version of PHP; auth_plugin_ldap has a deprecated constructor in /var/www/moodle29/auth/ldap/auth.php on line 86
Deprecated: Methods with the same name as their class will not be constructors in a future version of PHP; auth_plugin_mnet has a deprecated constructor in /var/www/moodle29/auth/mnet/auth.php on line 33
Deprecated: Methods with the same name as their class will not be constructors in a future version of PHP; mnet_encxml_parser has a deprecated constructor in /var/www/moodle29/mnet/xmlrpc/xmlparser.php on line 14
Deprecated: Methods with the same name as their class will not be constructors in a future version of PHP; mnet_peer has a deprecated constructor in /var/www/moodle29/mnet/peer.php on line 13
Deprecated: Methods with the same name as their class will not be constructors in a future version of PHP; mnet_environment has a deprecated constructor in /var/www/moodle29/mnet/environment.php on line 8
Dashboard...
Deprecated: Methods with the same name as their class will not be constructors in a future version of PHP; moodleform has a deprecated constructor in /var/www/moodle29/lib/formslib.php on line 124
Deprecated: Methods with the same name as their class will not be constructors in a future version of PHP; MoodleQuickForm has a deprecated constructor in /var/www/moodle29/lib/formslib.php on line 1370
Deprecated: Methods with the same name as their class will not be constructors in a future version of PHP; MoodleQuickForm_Renderer has a deprecated constructor in /var/www/moodle29/lib/formslib.php on line 2538
Deprecated: Methods with the same name as their class will not be constructors in a future version of PHP; HTML_QuickForm has a deprecated constructor in /var/www/moodle29/lib/pear/HTML/QuickForm.php on line 97
Deprecated: Methods with the same name as their class will not be constructors in a future version of PHP; HTML_QuickForm_Error has a deprecated constructor in /var/www/moodle29/lib/pear/HTML/QuickForm.php on line 1965
Deprecated: Methods with the same name as their class will not be constructors in a future version of PHP; PEAR has a deprecated constructor in /var/www/moodle29/lib/pear/PEAR.php on line 87
Deprecated: Methods with the same name as their class will not be constructors in a future version of PHP; PEAR_Error has a deprecated constructor in /var/www/moodle29/lib/pear/PEAR.php on line 796
Deprecated: Methods with the same name as their class will not be constructors in a future version of PHP; HTML_Common has a deprecated constructor in /var/www/moodle29/lib/pear/HTML/Common.php on line 39
Deprecated: Methods with the same name as their class will not be constructors in a future version of PHP; HTML_QuickForm_Renderer_Tableless has a deprecated constructor in /var/www/moodle29/lib/pear/HTML/QuickForm/Renderer/Tableless.php on line 45
Deprecated: Methods with the same name as their class will not be constructors in a future version of PHP; HTML_QuickForm_Renderer_Default has a deprecated constructor in /var/www/moodle29/lib/pear/HTML/QuickForm/Renderer/Default.php on line 31
Deprecated: Methods with the same name as their class will not be constructors in a future version of PHP; HTML_QuickForm_Renderer has a deprecated constructor in /var/www/moodle29/lib/pear/HTML/QuickForm/Renderer.php on line 29
Deprecated: Methods with the same name as their class will not be constructors in a future version of PHP; grade_plugin_return has a deprecated constructor in /var/www/moodle29/grade/lib.php on line 1090
Deprecated: Methods with the same name as their class will not be constructors in a future version of PHP; grade_seq has a deprecated constructor in /var/www/moodle29/grade/lib.php on line 2035
Deprecated: Methods with the same name as their class will not be constructors in a future version of PHP; grade_tree has a deprecated constructor in /var/www/moodle29/grade/lib.php on line 2172
Deprecated: Methods with the same name as their class will not be constructors in a future version of PHP; grade_export_update_buffer has a deprecated constructor in /var/www/moodle29/grade/export/lib.php on line 621
Deprecated: Methods with the same name as their class will not be constructors in a future version of PHP; moodleform_mod has a deprecated constructor in /var/www/moodle29/course/moodleform_mod.php on line 9
Deprecated: Methods with the same name as their class will not be constructors in a future version of PHP; table_default_export_format_parent has a deprecated constructor in /var/www/moodle29/lib/tablelib.php on line 1553
Course page... No Errors!!
Assignment...
Deprecated: Methods with the same name as their class will not be constructors in a future version of PHP; fpdi_pdf_parser has a deprecated constructor in /var/www/moodle29/mod/assign/feedback/editpdf/fpdi/fpdi_pdf_parser.php on line 22
Deprecated: Methods with the same name as their class will not be constructors in a future version of PHP; pdf_parser has a deprecated constructor in /var/www/moodle29/mod/assign/feedback/editpdf/fpdi/pdf_parser.php on line 51
Deprecated: Methods with the same name as their class will not be constructors in a future version of PHP; pdf_context has a deprecated constructor in /var/www/moodle29/mod/assign/feedback/editpdf/fpdi/pdf_context.php on line 22
...and so on...
So, at a very quick glance it seems to work but throws Deprecated notices all over the place. I suspect it'll be more or less ok with debugging off but how do you know for sure?