Lighting data : slowdown

I wasn’t having slowdown on startup in U 5.62

and recently noticed there’s a new folder created with lighing data
(it is 761M, so no wonder it slows down)

now I use U 5.64, but not sure if it hasn’t appeared now in U 5.62 project too

before:
3400166--267641--Clipboard03.jpg

now:
3400166--267642--Clipboard01.jpg

3400166--267643--Clipboard02.jpg

so the question is, how should I avoid it

also another thread, but no solution

okay, so what I did:

switched off realtime global illumination
and I don’t see any noticeable quality change
3400385--267668--Clipboard05.jpg

the folder is still generated but filesizes are small
3400385--267667--Clipboard06.jpg
and there’s no startup slowdown anymore