Is there a Mikrotik on both ends of the L2TP tunnel?
If so, an EoIP tunnel might be easier than L2TP. This point suggests that:
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That 2017 post above problem may be that HD was a 30-36Mb/s MPEG-TS "mux", but his bandwidth was only 27Mb/s – so EoIP seem to work, but yeah you'd need bandwidth.
L2TP is a bit more complex, but multicast PIM should work – if you have multiple L2TP links on the same router to same network get even more tricky. L2TP will compress the MTU, so you'd need to pay attention to how the IPTV stream if framed (e.g. 1427 + 14 RTP + 20+ for IP, get close L2TP default 1450 MTU)
If you want to be a ginny pig, V7 with ZeroTier should able to bridge the multicast, but different/untested approach.