Well, forgot to chime in when I first read the thread.
I wanted to tell you pretty much the same as abhishek. Especially SD cards nowadays are extremely optimized for huge files of several GB. If you have a lot of small files, this is what SD cards nowadays are least efficient at. What you experience is pretty normal.
That said, do you copy it directly to your SD card or do you copy it to your phone that has the SD card in it? This slows it additionally. Besides that, the CPU needs to handle some load too, so if you have a really old Laptop or just a weak one, this could also impact overall performance. Same with RAM.