Thanks for the advice, actually 10mg would probably have been more sensible in retrospect.
Apologies all, I don't intend to keep using this thread as some kind of running commentary/blog but I will just share my final experience of yesterday evening.
It does seem like 15mg for me is when things started to get weird. I was having a conversation over text with a friend of mine about our ambitions for the future, and fortunately what I was actually saying wasn't anything too weird but I remember my thought process and it was definitely starting to border on mania with some delusions of grandiosity about how I was going to change the world... despite the fact I was typing on an onscreen predictive text smartphone keyboard, which with K would quickly become incomprehensible and result in messages littered with spelling mistakes and nonsensical autocorrected word substitutions, it was like I couldn't get my ideas out fast enough but was still able to type with perfect accuracy using language with perfect clarity. I keep comparing this substance to K because it's really my only reference point but it really does strike me that this substance could not be more different to it's chemical cousin.
Anyway at about T+2 hours I distinctly remember the experience took a sudden and unexpected turn... suddenly I couldn't remember how to spell a word, I literally stopped what I was doing mid-sentence and the fact that I couldn't do this seemed to take on a huge significance. Over the next 20 minutes to half an hour (I know this from reading back my strange mid-sentence break in the conversation) I remember feeling distinctly uncomfortable and different, I could hear an incessant loud whine, almost like an alarm, like the characteristic otherworldly buzz of K turned up several frequencies and massively amplified.
I remember feeling like I was observing my own self-awareness, but also feeling very strongly that this sense of self awareness was not actually myself... like I was a being that had suddenly gained awareness of it's own sentience, and was able to observe the feeling that previously I had believed to constitute self-awareness... I remember thinking something like "if this (or that) is not me, then what am I?" ...or something along those lines, it's very hard to actually properly convey the feeling but I believe it was still a verbal thought (as in, spoken in my own internal monologue rather than a feeling alone).
This was a hugely bizarre sensation, and like nothing I have ever experienced before. I guess this is what would be called true "dissociation" but it's not something I've ever felt, at least not so acutely and in this way, on any other dissociative or indeed any other drug. It was not a pleasant sensation and did have quite a sinister tone to it, although I cannot put my finger on exactly why this is. I remember thinking also "so THIS is what psychosis feels like", although in retrospect this was almost certainly because of all the warnings I had read about 3-MeO-PCP's propensity to induce psychosis, so I don't know if this is actually what psychosis would feel like... anyway for reasons I am not exactly sure about, except perhaps an awareness that I was in a very atypical and uncomfortable state of mind I went digging in my drug stash for a 2mg bar of alprazolam, I broke it in half intending to take 1 mg, but then thought better of it and just set it on the table in front of me, and just made myself sit down in silent contemplation.
I couldn't say exactly what happened or what I was thinking after that but the feeling gradually subsided and I gradually came back to myself somewhat and tried to sleep a little later... I remember lying there feeling quite blank, buzzed and with occasional rushes of just maniacal happiness about nothing in particular.
Just as a brief addendum, at T+4.5 hours I unwisely decided to take 20mg zolpidem as it was late and I couldn't actually sleep (I don't usually have this many pharmaceuticals just lying around, I just happened to recently acquire a few things I have always been curious about).
This is something I will most definitely not do again but I ended up having a very bizarre but I believe mercifully brief trip where all the furniture in my room was moving around on it's own accord, or being moved by some faceless nameless entities. I don't know when this was, but I have a memory of overturning my coffee table, knocking a bunch of stuff on the floor, at which point I actually asked the entities, I believe out loud, to stop doing this and to please put everything back to how it was. Obviously they did not respond or do as I had asked, and I believe I realised at this point that obviously it was actually just myself moving things (possibly just the one aforementioned coffee table in a misguided effort to stop or undo the other imagined movements) so I sorted things out as best I could and finally stumbled into bed.