Lua is quite a bit larger than Tcl. In addition, no two Lua installations can ever agree on which modules they require (which makes the actual Lua binary even bigger).
Larger? On my system libtcl8.6.so is 1.7 megabytes and liblua5.1.so is 192 kilobytes. It's not even close. Lua uses libraries / modules based on where you tell the interpreter they are located, so that's on you.
Lua?
It's used in (and used for?) a lot of embedding:
* https://en.wikipedia.org/wiki/Lua_(programming_language)