Guys, its super cheap on Renta

They've chopped up the chapters into even smaller chapters (the first volume was a published manga.) So one chapter is actually 2-3 Renta chapters.

But ch 14 on Renta is the same Ch 14 here. Then what are Ch 15-20 on Renta?

I said the first volume. The second volume was only published online. The entire first volume (except for the first chapter) is divided into extra chapters on Renta. You can see for yourself since the original manga is posted here.