I have this same concern. I have to upgrade to PhP 5.5 (and frankly, 5.6 is out of support by Jan 01, 2017, so this is an old issue). Can bbPress be updated to work under PhP 5.5, or at least not throw an error?
Here are the full errors I received
FILE: /home/classics/public_html/wp-content/plugins/bbpress/includes/users/functions.php
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FOUND 1 ERROR AFFECTING 1 LINE
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1380 | ERROR | The function hash_equals is not present in PHP version 5.5 or earlier
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FILE: /home/classics/public_html/wp-content/plugins/bbpress/includes/admin/parser.php
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FOUND 2 ERRORS AND 1 WARNING AFFECTING 3 LINES
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1149 | ERROR | preg_replace() – /e modifier is deprecated since PHP 5.5
1150 | ERROR | preg_replace() – /e modifier is deprecated since PHP 5.5
1386 | WARNING | The use of function split is discouraged from PHP version 5.3; use preg_split instead
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FILE: /home/classics/public_html/wp-content/plugins/bbpress/includes/admin/converter.php
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FOUND 0 ERRORS AND 1 WARNING AFFECTING 1 LINE
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310 | WARNING | INI directive ‘safe_mode’ is deprecated from PHP 5.3 and forbidden from PHP 5.4.
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