slow transport, master.cf and maxproc value

[Myrdhin]

Hello,

I have this Postfix configuration : all mail destined for domain.tld are 
relayed by the "slow" transport.

# in main.cf :
transport_maps = hash:/etc/postfix/transport

# in /etc/postfix/transport
domain.tld slow:

# in master.cf :
slow      unix  -       -       n       -       5       smtp -v -o 
smtp_destination_concurrency_limit=3 -o slow_destination_rate_delay=1

I would like to know if the maximum connections defined in the slow 
transport are 3 or 15 (3 smtp_destination_concurrency_limit x 5 maxproc) ?

If it's 15, how could i configure Postfix to make 3 max connections ?
Perhaps like this ? :
slow      unix  -       -       n       -       3       smtp -v -o 
smtp_destination_concurrency_limit=1 -o slow_destination_rate_delay=1

Thanks for your help,
--
Myrdhin,