Small remark.
Nobody is forcing you to change ROS on those 16Mb Flash-devices.
They are perfectly usable on ROS6 (almost nothing has changed for legacy wifi in ROS7).
When you do not specifically change some setting, they will not even go search for ROS7 on their own. They will happily stay on ROS6.
Unless there is a very specific reason why you want to move to ROS7 ?
In that case you might also want to reconsider the HW being used since it is a known fact e.g. hap lite is not recommended for ROS7.
https://help.mikrotik.com/docs/display/ROS/Upgrading+to+v7
Note: We do not recommend running v7 on hardware that does not have at least 64 MB of RAM.
16Mb for storage might indeed be a deal breaker as well (though I have upgraded various AC3 models without any problem already to ROS7 since I needed wireguard and wifiwave2).
It may work, or not …