Pasir Ris Dr 1 in total has about 12 stops. It is rare that the
bus will complete this journey in 15 mins, given that aft PSR
Central stop only can take 2 mins given there are also other
services. I think the average time to cover this stretch should be
18-22 minutes.
To you and user "ButIAmAToilet", try taking a Sv 39 before
0645hrs during Weekdays from the first stop PSR Dr 1 in direction
of Yishun. There is a significant difference in their urgency to
make the required frequency before 0640 and after
0640hrs.
Ditto for the frequency during off-peak, which is closer to what
you said of 20+mins. And like what you had posted, what you
calculated is theoretical. There are quite a number of stops which
Sv 39 (or the svcs that pass by PSR Dr 1 on the side closer to Dr
12) tend to just skip along PSR Dr 1 during Off-peak (which is
another issue all together since it's not the timing I'm trying to
talk about).
Or if you guys would still like to doubt me, feel free to go
ahead. I take Sv 39 practically every weekday morning around
0630hrs so I was posting my own observations for the timing I sat
(which is usually 15mins+ to clear PSR Dr 1). 