Jay - good attempt indeed but I think there are 8 syllables in line 2 making the syllable count ,18 in all.
A senryu is 17 or less like a haiku. Keep going with thisone - almost there.
All the best
# edit - i see there are 4 and not 5 on the first line so it works! I would put 'stood' on line 1 to make the 5 7 5 count though

Hello,

The last shower
^
This sounds like a play on the phrase, 'the last supper' it sets this piece in the same light for me. A final liaison maybe? I like that this line says so much, yet leaves intrigue. A good first line as I always use the title to help explain the poem.

Denuded they
^
I admit I had to find out what this word meant. Bare, without cover - a good word and apt. I see more than one person in a shower as you have used the word, 'they'. This line needs another syllable.

stood huddled outside, one last time
^
okay, so a group or a pair of people outside in the rain. The word huddled suggest that they are remaining close to receive shelter from the weather. The addition of 'one last time' brings more intrigue and leads to the next line. There are one too many syllables here.

Exodus from kampf.
^
This last line should tie the previous two together and I must say that it made sense of the whole poem. The word Exodus paints a picture of a mass of exiting people with urgent purpose. The word 'Kampf' mean field and is linked to a book about Adolf Hitler. I am not sure if this is deliberate, but if it is it paints a totally different picture with intense emotion. I now see a group of prisoners in a concentration camp outside huddled trying to keep warm. Now I am unsure if they are about to be killed or if they are free, so I need more explanation before I can comment on the overall piece. What are you trying to say?

I have re-worked it slightly to make correct the syllable count only.

Denuded they stood
huddled outside one last time:
Exodus from kampf.
^
As you can see, just one change brings the count in perfectly.

All in all this is a good Senryu in which you have painted a vivid picture in which a mass of people, possibly prisoners huddled together having left a 'kampf' - are they moving to their death or are they free?

Please let me know.

Take care,

Michael