15 Bishoujo Hyouryuuki

Though the setting is different, both have the same protagonist on the hunt for all the girls around him in different situations. 

Similarities: - A guy surrounded by a harem of girls - The girls are each different and fit into different archetypes - The main characters are alone on a beach/island setting Differences: - Rescue Me! is borderline-H while 15 Bishoujo is a hentai 

Voyerism (filming/photo taking) in Joshikousei no Koshitsuki is the same as in 15 Bishoujo Hyouryuuki where the girl is actually okay with MC filming her and gives him a lot of sexy angles. Another similarities are pretty girls in bikini and also the fact that both shows have multiple waifus that change with each episode.  

A guy is on an island with a bunch of hot girls and uses his camera to get himself into their panties. In this hentai the camera does not make the girls horny. They end up doing things for him on film for "modeling" purposes. 

They fit as many fetishes as they can possibly fit into an OVA. Both have pretty good animation. Kagaku na Yatsura is just borderline hentai while 15 Bishoujo is a full-on hentai. 

One guy makes love to many girls. 

In several aspets these two serieses are similar. - Protagonists have cameras - They take pictures of/film a large harem of girls, be it in a school, or on a secluded island I guess the main difference would be the extent of peversion within the series. But from episode 2 of Photokano, i realised that these 2 animes are alike, even if 15BH is much less watered down.