For comparison, the current version of Lua is 5.4.
1. Lua from Modern Roblox - Legacy Roblox Wiki
I'd say this is good for people who already know modern Luau or non-Roblox Lua
2. Absolute beginner's guide to scripting - ROBLOX Wiki
I'd say this is good for people who don't already know Lua.
The archive of the ROBLOX Wiki is generally good for guides for old Roblox, in my opinion.
If you wish to watch a series of video tutorials rather than read a page and do not know Lua, there are plenty of options for you. The ones here were selected on the requirements of being made in 2015 or earlier, small text inside the videos being legible, and having 3 or more videos. The list below is ranked from oldest to newest.
1. Roblox Lua Tutorials (Samuel Silvester) - 2011 | 38 videos
2. Roblox Lua Scripting Tutorial (dev Lineout) - 2013 | 13 videos
3. Roblox Lua Scripting Tutorial (Roboslayer10) - 2013 | 15 videos
4. ROBLOX Lua Scripting Tutorial (Project Indie) - 2014 | 4 videos
5. ROBLOX Lua Scripting Tutorials (Wrathsong) - 2015 | 13 videos
If you're already at an intermediate or above level in Lua and would rather watch a series of video tutorials than read a page, then I think Wrathsong's ROBLOX Lua Intermediate Tutorials may be a good option, though they were made in 2017. I wasn't able to find any (specifically) intermediate-level tutorials from 2015 and earlier.
The links and/or list here may be updated in the future.
