I'm able to ping 180 network gateway (180.1) from network 20
This indicates that the .20. has a route to .180. via the address in .20. it assigns to the Mikrotik's DHCP client attached to ether1.
but can't ping the devices inside 180 network.
This together with the above suggests that the firewall filter on the Mikrotik itself accepts pings to Mikrotik's own IP addresses (chain
input):
action=accept chain=input comment="defconf: accept ICMP" protocol=icmp
but doesn't accepts ping requests to devices behind the Mikrotik (chain
forward). This is normal in the default SOHO configuration where it is not expected that incoming requests received at WAN should be forwarder to the LAN side.
So the next step is to explain what the final topology and setup should be - we can convert the Mikrotik into a regular "LAN-only" router that is not directly connected to internet nor it plays any firewalling role, i.e. firewalling is provided by Teltonika - in that case, you can remove the NAT rules and firewall filter rules at least in chain forward. Or you want it to act as a firewall for the devices in .180. and you have to modify the firewall filter rules accordingly rather than removing them. By removing the NAT, you'll lose even the possibility to initiate connections from .180. to .16. until you fix the next problem.
Anyway, I'm also experiencing Destination host unreachable when I ping network 180 from network 16.
If this includes also .180.1, all the possibilities I've suggested before remain valid. It may be missing routes, it may be a missing IPsec policy, it may be a firewall on either Teltonika.
So either post the configuration files from both Teltonikas (naming them in such a way that the original file name is extended with the site distinguisher such as .16 and .20) here, or ask at some Teltonika or OpenWRT forum (where guys will ask for those configuration files too).