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
KK, approx how long between the long rep, say 150m, then the shorter sprints of 60m and under.
I’m interested in trying this work. Up till now I’ve kept it simple, remembering a quote from Charlie that girls responded well to SE1 (sprints of 8-15s duration).