I'm not sure that it would feel like that much of a reduction. Whilst going from a train every 6 minutes to one every 15 would be an extra 9 minutes between services, due starters that's not all that much extra time and the fact that the trains would likely have more available seats would mean that in the peak (and maybe even at times of disruption) you could almost always just get the next train rather than potentially having to let some go past because they are so full.
I've previously commuted by train from a station just after a station with much faster services, even with fairly small populations (2 stains with less than 10,000 and the next one being 50,000) the trains in the peaks, even with 3tph or more, were full and standing upon leaving the third station.
Likewise I've worked somewhere with 4tph (off peak) and you never felt like you needed to time your departure from the office all that acutely to get the train to go to a meeting (you'd know that you needed the xx:15 or xx:30 at a push, but you'd leave about xx:05 but it wouldn't be a disaster if you left at xx:20). Even at 10tph it's not going to be much better.
However as you highlight in your edit, there's them potential to have new services to new places which might actually benefit a wider group of people.