OpenWRT was desined to support devices with low memory.
Now you are using new kernels which are "huge" I guess
Does this make sense?
If you cannot use programs like iptraf, iperf and so on I think you realy loos the reason why openwrt was used instead of stock firmware. I think stock firmwares are the same stable as opnwrt...
I used OpenWRT since Version 0.9 on a lot of devices.
I think you should try to have at least in parallel 2 kernels for new version, so devices with low memory can be also used...
Without luci it does not make sense.
LEDE worked still fine with lucy...
What you are asking is a lot like "My Pentium 90 system still boots. Why doesn't Windows 10 run on it?"
It is not only the flash that is the problem, but also the RAM and the CPU power. People expect and need more from routers that are generally a decade old (or under-spec-ed by an ODM to reach some price point) than they did in the days when a 25 Mbps line was considered screaming fast.
Have a lot of TP Link wr841 V8-V11 with 32/4 MiB .
Yes I have stripped down to the minimum I need to use this routers.
It seems that I have to stay with chaos-chalmer-15.05 and/or LEDE-17.01.4 to use all the nice stuff.
Just trying to compile OpenWRT-18.06.1 for wr841 V13 with 64/8 MiB
With LUCI complains about too big... even double rom (8MiB) as old ones...
I would strongly suggest 17.01 or later, as 15.05 has not been patched for security vulnerabilities for far too long.
While LuCI is "nice stuff" for many, it does have a large overhead in storage and RAM requirements that have little, if anything, to do with the choice of kernel. As you have "a lot" of these devices, another approach worth examining is implementing another way to manage them in bulk, such as ssh keys and appropriate scripts along with rsync or similar. snmpd may also be a possibility (though it is likely a few hundred kB in size).