It's one reasonably efficient line using the data as you currently have it:

#! perl -slw
use strict;

my @a = ( 1, 15, 30, 50, 65 );
my @b = ( 5, 20, 37, 55, 77 );
my( $s1, $s2 ) =( 9, 35 );

my @result = map{
    grep $_ >= $s1 && $_ <= $s2, $a[ $_ ] .. $b[ $_ ]
} 0 .. $#a;

print "@result";

__END__
C:\test>junk12
15 16 17 18 19 20 30 31 32 33 34 35
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