Volume 8 comes out this month.

After looking into it the WN's last update was on 2018/12/17. Looks like the author took a ~6 months break at the start of 2018, and he barely posted 19 chapters in the entire year. In total there are only 145 chapters, quite a low count, and they are rather short, too. Most likely it crams around 40~50 chapters per volume like Campire Cooking. Based on the above I'd say there is not enough content for a new volume yet.

Just read first volume and it was great, i would totaly buy something like that. Good game-isekai without op MC and Harem are too rare.