As noted here, a lower interval will give quicker connection - but at the expense of power consumption.
With a 4s interval, it seems that it is likely to take several "Scan" attempts (as in the Nordic demo apps) before the device will actually be "seen".
Is there any guidance on how the Advertising Interval affects the time to connect?
(I'm using nRF8001, but I guess that's not particularly relevant here?)