What confuses me is that the Luckfox Pico Mini B also doesn't come with an Ethernet port, so where does the IP address 192.168.0.15 come from?

For the Luckfox Pico Mini B without an Ethernet port, you can only use a USB virtual network interface for SSH login. Its static IP address is fixed at 172.32.0.93, so when configuring the virtual network interface on the computer, it should also be in the 172.32.0.xxx subnet.

Mine does. I designed custom board. I can ping ethernet but can not login via USB or ethernet.
UART terminal interaction. The default etho IP address is non responsive as well. With the exception of ping.

Luckfox:~# ifconfig
eth0 Link encap:Ethernet HWaddr CE:05:54:EF:8E:53
inet addr:192.168.50.59 Bcast:0.0.0.0 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:328 errors:0 dropped:0 overruns:0 frame:0
TX packets:21 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:20023 (19.5 KiB) TX bytes:882 (882.0 B)
Interrupt:51

lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
UP LOOPBACK RUNNING MTU:65536 Metric:1
RX packets:32 errors:0 dropped:0 overruns:0 frame:0
TX packets:32 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:2840 (2.7 KiB) TX bytes:2840 (2.7 KiB)

Luckfox:~#

I got the ethernet and login issues resolved. My pico minib is now on the network and is detecting my i2c interface as well. very cool.

[ 253.842454] rk_gmac-dwmac ffa80000.ethernet eth0: Link is Up - 100Mbps/Full - flow control rx/tx

# i2cdetect -a -y 3
0 1 2 3 4 5 6 7 8 9 a b c d e f
00: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
10: 10 -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: 20 -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
#

It turns out you soldered the Ethernet port yourself. Congratulations on successfully connecting to the network! That's fantastic! Feel free to share your Ethernet debugging process on the forum; I believe it will be helpful to many others.

how do i solder it. do you have a picture of the instructions? thank you