Is it possible to memorize most of my detailed study and general convo these holidays even though half the time I don't even know what I'm saying? My detailed study is around 6000 words and GC nearly 10000.
It depends imo; ones' ability to memorise is different for everybody, but if you're determined then it's possible

. Also, what do you mean when you say you don't understand what you're saying? Do you mean they're not your answers? Or that you respond with jibberish (trust me that's what I did for the majority of year 12, before I refined my answers)? Honestly it really helps to know what you're saying in that you at least understand the sentences you're going to respond with, as otherwise you're taking a big risk as the assessors could pick up on a part of your answer and ask you about it, so you NEED to be able to respond to these follow up questions to do well.
I have not even done my detailed study yet...am I behind?
By the way I'm just making things up for General conversation oh well .-.
At this stage I had about 2/3 of my detailed study done- most was done term 3 iirc. I wouldn't say you're behind, and you still have time before the oral exam! Just keep up consistent work and it'll be ok.
For your second statement/question/blah in a sense as long as you are at a level that you can respond fluently and spontaneously to a question asked, it doesn't matter if you improvise on the spot. In fact that's what we do in conversation with others in real life, and improvising answers is very likely to impress assessors, or in other words, memorising answers completely is limiting and is easily picked up by assessors (not saying memorising is bad, but if you memorise answers, don't fall for their traps if you know what I mean). I would still make sure you have a
basic idea of what you want to answer with though, for example for a question like 养宠物有什么好处?some ideas could be 1. 养宠物能让你心情大好 2. 养宠物还能培养孩子们的责任感和爱心以及社交能力 etc And these "ideas" could also be incorporated in similar questions.