Horde uses what is set in php.ini.
I have mine set to 35 MB
config show php
php=service
AllowUrlFopen=Off
MaxExecutionTime=1800
MemoryLimit=250M
PostMaxSize=35M
UploadMaxFilesize=35M
status=enabled
Make your db changes,
expand-template /etc/php.ini,
cat /etc/php.ini (Just to verify your changes are there)
signal-event email-update
Test
Thank you,
John