Hello,
The truth is that Premiere works with a lot of complicated codecs and has to jump through a few hoops to play and edit them.
What’s going on: The DSLR video/ AVCHD/ h.264/ mpeg4 is a tightly packed codec that Premiere has to 1) “index” (decode) and 2) “cache” (record and compare this index file in tandem during playback with the original file.
Waiting for it to index (lower right of screen will say “indexing” with a progress bar) and making sure it’s cached on a separate video capable drive(Edit/Preferences/Media)makes the difference between real time editing and what you’re experiencing.
Even an 8 core computer with loads of RAM needs a few minutes.
Tim