Can't change bridge subnet or create new network

I would like to build a small infrastructure entirely under Linux. For the LDAP and file server part I would like to set up a Docker server that will host the OpenLDAP and Owncloud containers. I would like to have a 10.10.15.0/24 network for my Docker server and its containers.
This will give :
Srv_Docker : 10.10.15.10
OpenLDAP : 10.10.15.1
Owncloud : 10.10.15.5

It is impossible to create a network with the addressing 10.10.15.0/24 because it seems that there is already a network with this addressing.
Creating a network with subnet 10.10.15.0/24

docker network create --subnet 10.10.15.0/24 --gateway 10.10.15.254 test
Error response from daemon: Pool overlaps with other one on this address space

ifconfig

ifconfig :
docker0: flags=4099<UP,BROADCAST,MULTICAST>  mtu 1500
        inet 10.10.15.1  netmask 255.255.0.0  broadcast 10.10.255.255
        ether 02:42:99:46:57:11  txqueuelen 0  (Ethernet)
        RX packets 0  bytes 0 (0.0 B)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 0  bytes 0 (0.0 B)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

eth0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet 10.10.15.10  netmask 255.255.255.0  broadcast 10.255.15.255
        inet6 fe80::20c:29ff:fe1d:9bc9  prefixlen 64  scopeid 0x20<link>
        ether 00:0c:29:1d:9b:c9  txqueuelen 1000  (Ethernet)
        RX packets 183  bytes 13477 (13.4 KB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 81  bytes 9002 (9.0 KB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
        device interrupt 19  base 0x2000

Network listing

Docker network ls 
NETWORK ID     NAME      DRIVER    SCOPE
6769af814ca4   bridge    bridge    local
91992f85bf6d   host      host      local
3d8f8aeefaf6   none      null      local

Bridge network display

docker inspect bridge :
                    "Subnet": "10.10.0.0/16",
                    "Gateway": "10.10.15.1"

Display OS version

cat /etc/lsb-release 
DISTRIB_ID=Ubuntu
DISTRIB_RELEASE=20.04
DISTRIB_CODENAME=focal
DISTRIB_DESCRIPTION="Ubuntu 20.04.5 LTS"

Display docker version

docker version
Version:          20.10.18