Looks right. I use small-small and then do exactly what you have done and try to use the longest length. If it is too long it will not properly clear. I would check with the existing chain length also.
I always give the chain a very good clean (instant debate) also, to get off all the storage grease you see in the photos.
The old chain is one link longer then this, but it was transfered from my old Pinarelo, and beeing in hurry to start riding my C60 as soon as possible, i asked a help from local shop to check chain, and to adjust properly deralieurs (and they did not adjust the front deralieur properly, and also the chain protector and i found that wrong way...), so im not sure if they adjusted the chain properly or it was easier for them just to install it without shortening.
BTW, existing chain length (one link longer), it's same number of links suggested by some chain length app (enter cogs, then chainstay length, and it's calculate number of links..
About cleaning the chain i had idea that is good to left this grease, but probably im wrong (i admit i did not analyze that properly until now).
I would go for as long as you can as this allows for running any cassette from the 11/23 up to the 11/29 without worrying about chain or causing excessive tension on the system when it is in big/big. In your case it looks like a judgement call since your two options are sort of at each extreme of long and short. If it were me, I would "possibly" go with the longer option even though it may be grazing the above pulley cage slightly when in the small small. Couple of caveats...1) When I say grazing, I mean grazing... not rubbing with any force. Since you should rarely, and possible never, be using the small/small combo, it should be ok. If it clears when it's on the second smallest cog that should be ok... provided 2) that there is at least some tension on the rear derailleur spring when it is in the small/small, even though it may be grazing a bit. Again, kind of a judement call that I would want to see and play with a bit in person before deciding. You'll likely be fine with the length you show, but I like it closer to 10mm than 15mm.
I experimented with this a lot when setting up my C60, and the longer option was best for my situation, although my choice was a lot clearer than yours. That's why I say yours is a judgement call. If it is too short, you may have difficulty adjusting the thing later so that you get the 5-7mm gap between the largest cog and the upper pulley when the chain is on the small chain ring up front.
I talked about that a fair bit in my build thread. Here's the link to the relevant post, you may want to read the couple of posts before it and after it for the complete story...viewtopic.php?f=10&t=142391&start=75#p1299386
Thanks Calnago for detailed post. On this chain i'll use only one cassette, and that is 11-29 Chorus i have. The chain im replacing was one link longer, but as i said it rubbing the cogs that way when small-small. I use sometimes that combination going on few deg downhill. I'll definetly read ur link, and also tommorow will post pics from small-small and big-big with one link longer.