Does anyone know how to get set 11, 15, and 17?

https://www.pixiv.net/user/2757608/series/43109

>how
You'd ask him to add you to his "my pixiv" (friend list thingy).
https://www.pixiv.help/hc/en-us/articles/235644287

Your request will be accepted or declined at his discretion. Considering that he have 140+ accounts on his list
https://www.pixiv.net/mypixiv_all.php?id=2757608
and most of them are just random disposal accounts with zero content submission, the qualification seems low. But you may have to be fluent in Japanese since the community do not like gaijins in general.

Base +12, pure_heart +7