Title says it all: from which version onward is the LimitRequestFieldSize no longer hardcoded to a max. of 8k?
It seems 2.2.15 is still affected.
Ok, so it turns out that it works in 2.2, but you need to increase the max AJP packet size if you have a Tomcat behind it and use mod_proxy_ajp, or else it will still give a 400 Bad Request.
Specifically, set this in Apache:
and this in Tomcat server.xml on the ajp connector:
Only setting LimitRequestFieldSize won't do the trick!