Depends on the individual. Also depends on how you site the propsoed SE1. Also on the specifics of the set/session.
But if you took the athlete out to, say, 120m or even 150m, you could do a pulse recovery (nothing moves until the pulse is under 130 bpmin.
Then, if the athlete feels up to it, perhaps you could use a descending ladder rather than another 150, which might be too taxing (ie: a split 300m). So you could look at aiming for 150m, 60, 50, 40, 30, 20 and in the descending dashes emphasise the Vertical rather than the Velocity - and eventually you will get both. But in this way, you are instilling a technical element to the training which is good in the long run, while excusing the novice from producing anything seering hot on the back-ups.
Eventually the set could look something like 20, 30, 40, 50, 60, 150 - jog remainder of the lap (250m as receover), then a second 150m, then a short recovery time before hitting the 60m, with walkbacks and into the 50m, 40, 30, 20. The shorter acceleration-style reps tend (hopefully) to discourage the athlete from kicking out the lower leg. Then you take that attacking action into the 150s without even thinking about it.
But a session like that - which I have used incorporating a third 150 - might be a few years away. And in the meanwhile, training as you see things, in my opinion. Delete any number of reps as suits. kk