Yes, not at all surprising. The TL-MR3020 falls into the category of low-flash, low-RAM devices that are challenging to impossible to run current firmware on.
For your application, I'd suggest purchasing a device with at least 16 MB of flash and 128 MB of memory. There are some out there for around US$20 that sound interesting in the What's your favourite cheap LEDE/OpenWrt device? thread.
I can't recommend any from personal experience (I buy used Archer C7 units for ~US$40) and I'm guessing you're looking for something small and compact. I've looked at the GL.iNet devices (mentioned in post #154) a couple times, but never gotten to the point of getting direct opinions about them from members that use them. The TRENDnet TEW-714TRU is interesting due to its plug-in format, but its 8/32 configuration would be very limiting for me.