@Rownan - as long as you're not likely to be demoralised by needing to reduce your pace a bit as the distance increases it's not a big deal. I wasn't and ended up quitting at, if I remember correctly, 7000m or 7500m because I couldn't keep up the pace I'd set on the first week
Where's the numbness by the way? I sometimes find the lower part of my right leg goes a bit numb, which suggests pressure on nerves servicing that area. Given my right hip is a bit misaligned (working on it) it's not all that surprising. It doesn't actually stop me from completing rows but it's pretty uncomfortable when it happens.
@Mitchel - obviously it's up to you, but I wouldn't feel bound to Pete's advice on rates. A lot of people do the three longer rows at lower rates than what he recommends (I used to do them at 18).
Good luck with the 5x1500m. My advice: try to pace each interval flatly (go out too fast and you'll pay for it), avoid trying to beat your target on the first four, and do at least some very light rowing between the intervals (I usually start rowing very lightly from about 4:30 remaining until 2:00 remaining). I find that if I don't do the last of these my body sort of shuts down and it makes the first ~300m of the next interval really unpleasant whilst my body restarts all the processes needed to burn energy.