FPS (frames per second) at 1 when joining a world

This has been happening since I joined minecraft on my new PC. 

So when I join minecraft, it is so slow as if a big tnt explosion that slows that game down happens. it usaly goes on for about 10-15 minutes before it gets better.

What I learned today was that my FPS was at 1-2-3-4-5 when I join and only gets up to 60-75 FPS after 10-15 minutes. Any Ideas why this occurs? Can it be fixed?