I did some googling and I see that this guy, seems to have the answer to your question.
After 15 minutes of research I ended up figuring out that this was due
to the PHP PDO constructor (my Firewall is the first to connect to the
database as I use Entities as users). With this knowledge the issue
was pretty quickly found ([1], [2]): as it turns out
using a DNS name (like ‘localhost’) instead of an IP (like
‘127.0.0.1’) causes this issue.A simple edit of the parameters.yml file (changing localhost to
127.0.0.1) did the trick of reducing the Firewall load time to only a minimum.