Try
vim.tiny -u NONE
For a smaller vim with less features. 3.9mb on my system. I don't have the original vi to compare, but when we are getting this small, any further memory savings are just noise, unless your dev box is a strange device. I doubt original vi would be faster than tiny vim.
Also try mg. Only a tiny bit larger than ed, but supports modern screen display and Emacs key binds. 1.1mb on my system. Screaming fast.
Also try GNU Emacs. It takes a bit of fiddling, but you can off-load much of the start-up slowness into the build stage. Loading things into the lisp image of temacs (at the cost of flexibility, you must rebuild when stuff changes if you want to keep the speed). Then you have a fully featured IDE that boots up in 0.2 seconds. Not bad and quite a bit faster than some tricked out Vim IDE's. You can have syntax highlighting turned off too, for more speed at runtime. Large, but it's in charge and not slow.