How long does it take you to plan, practice, and record a mix?

I was just asked to do 15 minute mix by a DJ friend of mine who wants to send it to this local promotional agency sort of thing, mainly EDM. This means in 15 minutes i need to show off a bunch of genres, at my best mixing, etc. I'm going from House to Dubstep to DnB to Hip-Hop/Rap to Moombah, so a lot planning is sort of required

I've been working on it everyday for about 4 days now, and am just now finishing up finalizing the tracklist, and will soon begin the process of planning each transition, making revisions here and there, practicing, and then finally recording. Hell I'll spend 30 minutes to an hour just trying to find the perfect mix between 2 songs.

He messages me today like, are you done yet, and I told him that I am only just about to finish track planning, he was sort of surprised I wasn't finished yet, and it always takes me this long to make a mix. I thought as I got better i would be quicker at it, but as I get better I only get more creative with it, so the time it takes hasn't changed much at all haha..

So, 4 days of mixing, a couple hours each day, only just now finishing up a tracklist.
Am I just really slow? Or is this just the time it takes to create a solid, good sounding mix.