This is because the OS takes time to fetch the file. Once fetched, the read is seamless. I had suggested to Adobe to use a read ahead algorithm. Once you play a sequence, it is obvious that the next clip will most likely be played. Unless you are jumping the play head back and forth. IMHO, Adobe should implement this feature.
However, 10 seconds is a bit too long. Please check if you have a slow ailing HDD or a fragmented one. You may need to defragment it.