On my system it took 60Mb:

ls -l ~/.local/share/kscreen
total 66244
-rw-rw-r-- 1 midenok midenok      953 Jan 31  2017 13eec7f52f0ecbc7e8695dec322a39b5
-rw-rw-r-- 1 midenok midenok      478 Jan 22  2017 2ce5ed0ef82f8319a76c25501b2e0807
-rw-rw-r-- 1 midenok midenok      477 Sep 23  2018 a4338ac837e495e1bdf276f4219511a4
-rw-rw-r-- 1 midenok midenok      865 Jul 26 21:39 ae7bd90cff431caa6561b22e8d877907
-rw-rw-r-- 1 midenok midenok      775 Mar 11  2017 c06d00ed3e679c7d8781ef63fb7c2d8e
-rw-rw-r-- 1 midenok midenok      416 Jul 24 03:57 c21f969b5f03d33d43e04f8f136e7682
-rw-rw-r-- 1 midenok midenok      950 Sep 27  2017 ee7b4cf60644c05581524ed9824d891b
-rw-rw-r-- 1 midenok midenok 67802009 Jul  2  2017 kscreen.log