Linux VM as gateway for tablet in same network

I want to sniff some traffic from my tablet. I though that I can do that by creating proxy server and route all trafic via it (using mitmproxy). Sounds easy but I struggle a lot. My current config is:PC with Virtual box VM (Ubuntu) and bridged network, android tablet, all devices are using same network and got inteet access via default gateway (192.168.1.1), ips are:
192.168.1.15 my PC
192.168.1.16 my VM ubuntu
192.168.1.17 tablet.

I changed gateway ip on tablet to be 192.168.1.16 tried, and inteet didnt work. then I tued on ip forwarding on ubuntu
echo 1 > /proc/sys/net/ipv4/ip_forward

tried, nothing worked again. Read more and added forwarding to iptables:
iptables -t nat -A POSTROUTING -j MASQUERADE

but still no connection from tablet to inteet.

then friend of mine suggested to also add route to VM:
route add -net 192.168.0.0/16 dev eth0

but again, no inteet on tablet. i can ping vm from tablet and from PC so it is visible in network.

my first question is.. it is enough for VM to have only one network interface? or it need another one? (maybe that is an issue) i am quite noob in networking so looking for some help.

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