No I've never had this request and I don't charge for shower expecting the client to have a quick wash but of he wants to take 15 minutes to freshen up then I would be annoyed and I don't think feeling annoyed is ever a good start to a booking. If he's offering to pay more though then that's up to him x

The OP says he's indicated he'll pay more, so I'd offer him a couple of options - explain you are sure he'll be clean enough and that over washing can be as damaging and unsexy as underwashing, that you can bring the appointment forward and can accomodate the 5mins a shower usually takes, or if he is saying he needs 15 minutes plus the 1 hour booked then agree a rate for 75 minutes or offer him a 90 minute appointment.

I've had the odd person disappear into the bathroom for what seems like hours, lots of clattering, rustling, usually coming out in a bit of a fluster after trying to give themselves a top to toe scrub from the contents of their small bag, and they tend to include that in their own time. Most people I find if they've had a shower within a few hours, or even that day(depending upon exact individual activities) tend to be clean enough - too much cleaning I find renders a human being devoid of natural oils and smells, and the skin of an over scrubbed cock takes on a pale, rubbery consistency. Makes it feel like the person has been dehumanified.

Thanks for your responses! I will offer him a longer booking for the extra pay.
Before I offer that I will tell him that a few minutes in the shower before and after is not in the one hour appointment. Up to him if he still needs 15 minutes bathroom time. And like one of you said, being annoyed at the start of our session is not a good way to begin...

Sometimes I had clients who indeed took forever afterwards. I am a part timer so no new appointment lined up but still.... I get very annoyed when it takes them forever and I hear a lot of noise and water going through my entire bathroom 

Good morning!

The appointment went really well. He paid 200, hardly showered and we had a good time :-). He emailed afterwards he enjoyed himself very much and our appointment was what he expected (I offer soft dom services). One happy customer! 

And now I have to go to my day job in the office. Which I enjoy most of the time, but now there is too much stress. At these times I think of working part time in the office and take more appointments. Especially when I received such nice feedback. Ah well.... drifting away from my own topic....

Perhaps he is someone who is a bit OCD so knows he can take at least this long in the shower. I would just let him know that a quick shower is no extra charge but if he knows he is going to be that long or longer then so he doesnt feel rushed he can just pay an extra ?20 or something, that way he will feel comfortable in knowing he doesnt have to rush his shower. Perhaps he comes very quickly so wants to knock one out in the shower when he arrives so feels guilty but doesnt want to admit it to you lol x