def range_to_arr_1(range, step=15.seconds)
  range.step(step)
end

def range_to_arr_2(range, step=15.seconds)
  [].tap do |a|
    date = range.begin
    stop = range.end
    while date < stop do
      a << date
      date += step
    end
  end
end

r1 = Time.now...Time.now+15.minutes
r2 = Time.zone.now...Time.zone.now+15.minutes
n1 = 150
n2 = 150

Benchmark.bm do |x|
  x.report { for i in 1..n1; range_to_arr_1(r1); 1; end }
  x.report { for i in 1..n1; range_to_arr_2(r1); 1; end }
  x.report { for i in 1..n2; range_to_arr_1(r2); 1; end }
  x.report { for i in 1..n2; range_to_arr_2(r2); 1; end }
end

#      user     system      total        real
#  0.280000   0.030000   0.310000 (  0.308992)
#  0.090000   0.000000   0.090000 (  0.092182)
# 10.500000   0.000000  10.500000 ( 10.505025)
#  0.210000   0.000000   0.210000 (  0.206929)