Swimming training

They refer to yards or meters depending on what the pool you're swimming in is measured. This is a standard convention for swim workouts because lap pools in the US typically come in one of 3 lengths: 25 yards, 25 meters or 50 meters.

My first day for training is supposed to be the warm up: 200 200 200 200 (800 lengths or meters/yards) Then there is a 1500 length. This is a lot. I had a hard time getting through just the warm up.

Any suggestions?

How has your swim training looked like a month prior to the plan?  Your doing the full 2mile IM swim for your race correct? Since it seems you have a lot of 'building to do' for 2.4 miles and have to get in ~4000meters/yards, AT LEAST do the time alloted if you can...even if you can't get through the complete workouts.  If you can't do the full time, that's ok, do what you can without killing yourself.  MAYBE add in an extra day of swiming for the first month or two to get up to speed faster.